diff --git a/crates/horizon-client/src/dialog.rs b/crates/horizon-client/src/dialog.rs
new file mode 100644
index 000000000..7acd3e86a
--- /dev/null
+++ b/crates/horizon-client/src/dialog.rs
@@ -0,0 +1,794 @@
+//! Server dialogs (`net.minecraft.server.dialog`): what `Dialog.DIRECT_CODEC`
+//! decodes from a `show_dialog` packet, the values its inputs hold, and the
+//! click event an action makes of them (`Action.createAction`).
+use crate::text::Text;
+use horizon_world::nbt::Tag;
+use serde_json::{Value, json};
+
+/// `CommonDialogData` and the type's own fields.
+#[derive(Clone, Debug)]
+pub struct Dialog {
+    pub kind: Kind,
+    pub title: Text,
+    pub external_title: Option<Text>,
+    pub can_close_with_escape: bool,
+    pub pause: bool,
+    pub after_action: AfterAction,
+    pub body: Vec<Body>,
+    pub inputs: Vec<Input>,
+}
+
+/// The dialog types (`DialogTypes`).
+#[derive(Clone, Debug)]
+pub enum Kind {
+    /// `NoticeDialog`: one button, "OK" when the server names none.
+    Notice(Button),
+    Confirmation {
+        yes: Button,
+        no: Button,
+    },
+    MultiAction {
+        actions: Vec<Button>,
+        exit: Option<Button>,
+        columns: i32,
+    },
+    ServerLinks {
+        exit: Option<Button>,
+        columns: i32,
+        button_width: i32,
+    },
+    /// `DialogListDialog`: its dialogs as sent (ids, a tag or inline dialogs).
+    DialogList {
+        dialogs: Tag,
+        exit: Option<Button>,
+        columns: i32,
+        button_width: i32,
+    },
+}
+
+/// `DialogAction`: the screen after an action runs.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum AfterAction {
+    Close,
+    None,
+    WaitForResponse,
+}
+
+/// `ActionButton`: `CommonButtonData` and what it does.
+#[derive(Clone, Debug)]
+pub struct Button {
+    pub label: Text,
+    pub tooltip: Option<Text>,
+    pub width: i32,
+    pub action: Option<Action>,
+}
+
+/// `Action`: a fixed click event, or one made from the inputs' values.
+#[derive(Clone, Debug, PartialEq)]
+pub enum Action {
+    /// `StaticAction`: a click event as it is.
+    Static(Click),
+    /// `CommandTemplate`: a command with `$(key)` replaced by input values.
+    RunCommand(String),
+    /// `CustomAll`: a custom click event whose payload is `additions` plus
+    /// every input's value under its key.
+    Custom { id: String, additions: Option<Tag> },
+}
+
+/// `ClickEvent`, the kinds a server may send (`isAllowedFromServer`).
+#[derive(Clone, Debug, PartialEq)]
+pub enum Click {
+    OpenUrl(String),
+    RunCommand(String),
+    SuggestCommand(String),
+    /// The dialog: an id of the `minecraft:dialog` registry or the dialog itself.
+    ShowDialog(Tag),
+    ChangePage(i32),
+    CopyToClipboard(String),
+    Custom {
+        id: String,
+        payload: Option<Tag>,
+    },
+}
+
+/// `DialogBody`.
+#[derive(Clone, Debug)]
+pub enum Body {
+    /// `PlainMessage`: centred text wrapped to `width`.
+    Message { contents: Text, width: i32 },
+    /// `ItemBody`: the item as `ItemStackTemplate` sent it.
+    Item {
+        item: Tag,
+        description: Option<(Text, i32)>,
+        show_decorations: bool,
+        show_tooltip: bool,
+        width: i32,
+        height: i32,
+    },
+}
+
+/// `Input`: the key its value goes by, and its control.
+#[derive(Clone, Debug)]
+pub struct Input {
+    pub key: String,
+    pub control: Control,
+}
+
+/// `InputControl`.
+#[derive(Clone, Debug)]
+pub enum Control {
+    Text {
+        width: i32,
+        label: Text,
+        label_visible: bool,
+        initial: String,
+        max_length: i32,
+        /// `MultilineOptions`: the most lines and the height, when set.
+        multiline: Option<(Option<i32>, Option<i32>)>,
+    },
+    Boolean {
+        label: Text,
+        initial: bool,
+        on_true: String,
+        on_false: String,
+    },
+    SingleOption {
+        width: i32,
+        /// Each option's id, its label and whether it is the initial one.
+        options: Vec<(String, Option<Text>, bool)>,
+        label: Text,
+        label_visible: bool,
+    },
+    NumberRange {
+        width: i32,
+        label: Text,
+        label_format: String,
+        start: f32,
+        end: f32,
+        initial: Option<f32>,
+        step: Option<f32>,
+    },
+}
+
+/// What an input holds while the dialog is open.
+#[derive(Clone, Debug, PartialEq)]
+pub enum InputValue {
+    Text(String),
+    Bool(bool),
+    /// The chosen option's index.
+    Option(usize),
+    /// The slider's position, 0 to 1.
+    Slider(f32),
+}
+
+fn text(t: &Tag) -> Text {
+    crate::scoreboard::comp_text(&crate::scoreboard::tag_to_json(t))
+}
+fn string(t: Option<&Tag>) -> Option<String> {
+    match t? {
+        Tag::String(s) => Some(s.to_string_lossy()),
+        _ => None,
+    }
+}
+fn number(t: Option<&Tag>) -> Option<f64> {
+    Some(match t? {
+        Tag::Byte(v) => f64::from(*v),
+        Tag::Short(v) => f64::from(*v),
+        Tag::Int(v) => f64::from(*v),
+        Tag::Long(v) => *v as f64,
+        Tag::Float(v) => f64::from(f32::from_bits(*v)),
+        Tag::Double(v) => f64::from_bits(*v),
+        _ => return None,
+    })
+}
+fn int(t: &Tag, key: &str, default: i32) -> i32 {
+    number(t.get(key)).map_or(default, |v| v as i32)
+}
+fn boolean(t: &Tag, key: &str, default: bool) -> bool {
+    number(t.get(key)).map_or(default, |v| v != 0.0)
+}
+fn list(t: Option<&Tag>) -> &[Tag] {
+    match t {
+        Some(Tag::List(items)) => items,
+        _ => &[],
+    }
+}
+/// A registry name without its default namespace.
+fn path(id: &str) -> &str {
+    id.strip_prefix("minecraft:").unwrap_or(id)
+}
+
+impl Button {
+    /// `ActionButton.CODEC`.
+    fn parse(t: &Tag) -> Option<Self> {
+        Some(Self {
+            label: text(t.get("label")?),
+            tooltip: t.get("tooltip").map(text),
+            width: int(t, "width", 150),
+            action: t.get("action").and_then(Action::parse),
+        })
+    }
+    /// `NoticeDialog.DEFAULT_ACTION`.
+    fn ok() -> Self {
+        Self {
+            label: Text::translate("gui.ok", &[]),
+            tooltip: None,
+            width: 150,
+            action: None,
+        }
+    }
+}
+
+impl Click {
+    /// `ClickEvent.CODEC`, from its `action` (a click event in a component)
+    /// or `type` (an action) field.
+    pub fn parse(t: &Tag, kind: &str) -> Option<Self> {
+        let s = |key| string(t.get(key));
+        Some(match path(kind) {
+            "open_url" => Self::OpenUrl(s("url")?),
+            "run_command" => Self::RunCommand(s("command")?),
+            "suggest_command" => Self::SuggestCommand(s("command")?),
+            "show_dialog" => Self::ShowDialog(t.get("dialog")?.clone()),
+            "change_page" => Self::ChangePage(int(t, "page", 1)),
+            "copy_to_clipboard" => Self::CopyToClipboard(s("value")?),
+            "custom" => Self::Custom {
+                id: s("id")?,
+                payload: t.get("payload").cloned(),
+            },
+            _ => return None,
+        })
+    }
+}
+
+impl Action {
+    /// `Action.CODEC`, dispatched on `type`.
+    fn parse(t: &Tag) -> Option<Self> {
+        let kind = string(t.get("type"))?;
+        Some(match path(&kind) {
+            "dynamic/run_command" => Self::RunCommand(string(t.get("template"))?),
+            "dynamic/custom" => Self::Custom {
+                id: string(t.get("id"))?,
+                additions: t.get("additions").cloned(),
+            },
+            other => Self::Static(Click::parse(t, other)?),
+        })
+    }
+    /// `createAction`: the click event, given each input's key, control and value.
+    pub fn click(&self, inputs: &[Input], values: &[InputValue]) -> Option<Click> {
+        let values = || inputs.iter().zip(values);
+        Some(match self {
+            Self::Static(click) => click.clone(),
+            Self::RunCommand(template) => Click::RunCommand(substitute(template, &|key| {
+                values()
+                    .find(|(i, _)| i.key == key)
+                    .map(|(i, v)| i.control.substitution(v))
+            })),
+            Self::Custom { id, additions } => {
+                let mut tag = match additions {
+                    Some(t @ Tag::Compound(_)) => t.clone(),
+                    _ => Tag::Compound(Default::default()),
+                };
+                for (input, value) in values() {
+                    if let Tag::Compound(map) = &mut tag {
+                        map.insert(input.key.as_str().into(), input.control.tag(value));
+                    }
+                }
+                Click::Custom {
+                    id: id.clone(),
+                    payload: Some(tag),
+                }
+            }
+        })
+    }
+}
+
+/// `ParsedTemplate.instantiate`: each `$(key)` replaced by its value, or by
+/// nothing for a key no input has.
+fn substitute(template: &str, value: &dyn Fn(&str) -> Option<String>) -> String {
+    let mut out = String::new();
+    let mut rest = template;
+    while let Some(at) = rest.find("$(") {
+        let Some(end) = rest[at..].find(')') else {
+            break;
+        };
+        out.push_str(&rest[..at]);
+        out.push_str(&value(&rest[at + 2..at + end]).unwrap_or_default());
+        rest = &rest[at + end + 1..];
+    }
+    out.push_str(rest);
+    out
+}
+
+/// `StringTag.escapeWithoutQuotes`.
+fn escape(s: &str) -> String {
+    let mut out = String::with_capacity(s.len());
+    for c in s.chars() {
+        match c {
+            '"' | '\'' | '\\' => {
+                out.push('\\');
+                out.push(c);
+            }
+            '\u{8}' => out.push_str("\\b"),
+            '\t' => out.push_str("\\t"),
+            '\n' => out.push_str("\\n"),
+            '\u{c}' => out.push_str("\\f"),
+            '\r' => out.push_str("\\r"),
+            c if c < ' ' => out.push_str(&format!("\\x{:02x}", c as u32)),
+            c => out.push(c),
+        }
+    }
+    out
+}
+
+impl Control {
+    /// `InputControl.MAP_CODEC`, dispatched on `type`.
+    fn parse(t: &Tag) -> Option<Self> {
+        let label = || t.get("label").map(text);
+        Some(match path(&string(t.get("type"))?) {
+            "text" => Self::Text {
+                width: int(t, "width", 200),
+                label: label()?,
+                label_visible: boolean(t, "label_visible", true),
+                initial: string(t.get("initial")).unwrap_or_default(),
+                max_length: int(t, "max_length", 32),
+                multiline: t.get("multiline").map(|m| {
+                    let get = |key| number(m.get(key)).map(|v| v as i32);
+                    (get("max_lines"), get("height"))
+                }),
+            },
+            "boolean" => Self::Boolean {
+                label: label()?,
+                initial: boolean(t, "initial", false),
+                on_true: string(t.get("on_true")).unwrap_or_else(|| "true".into()),
+                on_false: string(t.get("on_false")).unwrap_or_else(|| "false".into()),
+            },
+            "single_option" => Self::SingleOption {
+                width: int(t, "width", 200),
+                // SingleOptionInput.Entry.CODEC: a full entry or just its id.
+                options: list(t.get("options"))
+                    .iter()
+                    .filter_map(|o| match o {
+                        Tag::String(id) => Some((id.to_string_lossy(), None, false)),
+                        o => Some((
+                            string(o.get("id"))?,
+                            o.get("display").map(text),
+                            boolean(o, "initial", false),
+                        )),
+                    })
+                    .collect(),
+                label: label()?,
+                label_visible: boolean(t, "label_visible", true),
+            },
+            "number_range" => {
+                let float = |key| number(t.get(key)).map(|v| v as f32);
+                Self::NumberRange {
+                    width: int(t, "width", 200),
+                    label: label()?,
+                    label_format: string(t.get("label_format"))
+                        .unwrap_or_else(|| "options.generic_value".into()),
+                    start: float("start")?,
+                    end: float("end")?,
+                    initial: float("initial"),
+                    step: float("step"),
+                }
+            }
+            _ => return None,
+        })
+    }
+    /// The value it starts with.
+    pub fn initial(&self) -> InputValue {
+        match self {
+            Self::Text { initial, .. } => InputValue::Text(initial.clone()),
+            Self::Boolean { initial, .. } => InputValue::Bool(*initial),
+            Self::SingleOption { options, .. } => {
+                InputValue::Option(options.iter().position(|o| o.2).unwrap_or(0))
+            }
+            Self::NumberRange {
+                start,
+                end,
+                initial,
+                ..
+            } => InputValue::Slider(to_slider(
+                initial.unwrap_or((start + end) / 2.0),
+                *start,
+                *end,
+            )),
+        }
+    }
+    /// `ValueGetter.asTemplateSubstitution`.
+    pub fn substitution(&self, value: &InputValue) -> String {
+        match (self, value) {
+            (Self::Text { .. }, InputValue::Text(s)) => escape(s),
+            (
+                Self::Boolean {
+                    on_true, on_false, ..
+                },
+                InputValue::Bool(b),
+            ) => if *b { on_true } else { on_false }.clone(),
+            (Self::SingleOption { options, .. }, InputValue::Option(i)) => {
+                options.get(*i).map(|o| o.0.clone()).unwrap_or_default()
+            }
+            (Self::NumberRange { .. }, InputValue::Slider(_)) => {
+                number_string(self.scaled(value).unwrap_or(0.0))
+            }
+            _ => String::new(),
+        }
+    }
+    /// `ValueGetter.asTag`.
+    pub fn tag(&self, value: &InputValue) -> Tag {
+        match (self, value) {
+            (Self::Boolean { .. }, InputValue::Bool(b)) => Tag::Byte(i8::from(*b)),
+            (Self::NumberRange { .. }, _) => {
+                Tag::Float(self.scaled(value).unwrap_or(0.0).to_bits())
+            }
+            (Self::Text { .. }, InputValue::Text(s)) => Tag::String(s.as_str().into()),
+            _ => Tag::String(self.substitution(value).as_str().into()),
+        }
+    }
+    /// `RangeInfo.computeScaledValue`: a number range's value at its slider position.
+    pub fn scaled(&self, value: &InputValue) -> Option<f32> {
+        let (
+            Self::NumberRange {
+                start,
+                end,
+                initial,
+                step,
+                ..
+            },
+            InputValue::Slider(slider),
+        ) = (self, value)
+        else {
+            return None;
+        };
+        let (start, end) = (*start, *end);
+        let in_range = start + slider * (end - start);
+        let Some(step) = step else {
+            return Some(in_range);
+        };
+        let first = initial.unwrap_or((start + end) / 2.0);
+        // Math.round: half up.
+        let steps = ((in_range - first) / step + 0.5).floor() as i32;
+        let result = first + steps as f32 * step;
+        let position = to_slider(result, start, end);
+        if (0.0..=1.0).contains(&position) {
+            return Some(result);
+        }
+        Some(first + (steps - steps.signum()) as f32 * step)
+    }
+}
+
+/// `RangeInfo.scaledValueToSlider`.
+fn to_slider(value: f32, start: f32, end: f32) -> f32 {
+    if start == end {
+        0.5
+    } else {
+        (value - start) / (end - start)
+    }
+}
+
+/// `SliderImpl.valueToString`: whole numbers without a fraction, the rest as
+/// Java's `Float.toString`.
+pub fn number_string(v: f32) -> String {
+    if v == (v as i32) as f32 {
+        (v as i32).to_string()
+    } else {
+        crate::snbt::java_float(v)
+    }
+}
+
+impl Body {
+    /// `DialogBody.DIALOG_BODY_CODEC`.
+    fn parse(t: &Tag) -> Option<Self> {
+        let message = |t: &Tag| -> Option<(Text, i32)> {
+            // PlainMessage.CODEC: the full form or just its contents.
+            match t {
+                Tag::Compound(_) if t.get("contents").is_some() => {
+                    Some((text(t.get("contents")?), int(t, "width", 200)))
+                }
+                t => Some((text(t), 200)),
+            }
+        };
+        Some(match path(&string(t.get("type"))?) {
+            "plain_message" => {
+                let (contents, width) = message(t)?;
+                Self::Message { contents, width }
+            }
+            "item" => Self::Item {
+                item: t.get("item")?.clone(),
+                description: t.get("description").and_then(message),
+                show_decorations: boolean(t, "show_decorations", true),
+                show_tooltip: boolean(t, "show_tooltip", true),
+                width: int(t, "width", 16),
+                height: int(t, "height", 16),
+            },
+            _ => return None,
+        })
+    }
+}
+
+impl Dialog {
+    /// `Dialog.DIRECT_CODEC`; `None` for a type or field it can't read
+    /// (vanilla fails the whole packet then).
+    pub fn parse(t: &Tag) -> Option<Self> {
+        let button = |key: &str| t.get(key).and_then(Button::parse);
+        let kind = match path(&string(t.get("type"))?) {
+            "notice" => Kind::Notice(match t.get("action") {
+                Some(b) => Button::parse(b)?,
+                None => Button::ok(),
+            }),
+            "confirmation" => Kind::Confirmation {
+                yes: button("yes")?,
+                no: button("no")?,
+            },
+            "multi_action" => Kind::MultiAction {
+                actions: list(t.get("actions"))
+                    .iter()
+                    .map(Button::parse)
+                    .collect::<Option<Vec<_>>>()
+                    .filter(|a| !a.is_empty())?,
+                exit: button("exit_action"),
+                columns: int(t, "columns", 2),
+            },
+            "server_links" => Kind::ServerLinks {
+                exit: button("exit_action"),
+                columns: int(t, "columns", 2),
+                button_width: int(t, "button_width", 150),
+            },
+            "dialog_list" => Kind::DialogList {
+                dialogs: t.get("dialogs")?.clone(),
+                exit: button("exit_action"),
+                columns: int(t, "columns", 2),
+                button_width: int(t, "button_width", 150),
+            },
+            _ => return None,
+        };
+        // DialogBody.COMPACT_LIST_CODEC: one body, or a list of them.
+        let body = match t.get("body") {
+            Some(Tag::List(items)) => items.iter().filter_map(Body::parse).collect(),
+            Some(one) => Body::parse(one).into_iter().collect(),
+            None => Vec::new(),
+        };
+        let inputs = list(t.get("inputs"))
+            .iter()
+            .filter_map(|i| {
+                Some(Input {
+                    key: string(i.get("key"))?,
+                    control: Control::parse(i)?,
+                })
+            })
+            .collect();
+        Some(Self {
+            kind,
+            title: text(t.get("title")?),
+            external_title: t.get("external_title").map(text),
+            can_close_with_escape: boolean(t, "can_close_with_escape", true),
+            pause: boolean(t, "pause", true),
+            after_action: match string(t.get("after_action")).as_deref() {
+                Some("none") => AfterAction::None,
+                Some("wait_for_response") => AfterAction::WaitForResponse,
+                _ => AfterAction::Close,
+            },
+            body,
+            inputs,
+        })
+    }
+    /// `onCancel`: what Escape (or closing it) does.
+    pub fn on_cancel(&self) -> Option<&Action> {
+        match &self.kind {
+            Kind::Notice(b) => b.action.as_ref(),
+            Kind::Confirmation { no, .. } => no.action.as_ref(),
+            Kind::MultiAction { exit, .. }
+            | Kind::ServerLinks { exit, .. }
+            | Kind::DialogList { exit, .. } => exit.as_ref().and_then(|b| b.action.as_ref()),
+        }
+    }
+    /// The buttons it draws, in order: the list, then the footer's.
+    pub fn buttons(&self) -> Vec<&Button> {
+        match &self.kind {
+            Kind::Notice(b) => vec![b],
+            Kind::Confirmation { yes, no } => vec![yes, no],
+            Kind::MultiAction { actions, exit, .. } => actions.iter().chain(exit).collect(),
+            Kind::ServerLinks { exit, .. } | Kind::DialogList { exit, .. } => exit.iter().collect(),
+        }
+    }
+    /// What `status` reports of it.
+    pub fn json(&self, values: &[InputValue]) -> Value {
+        let kind = match &self.kind {
+            Kind::Notice(_) => "notice",
+            Kind::Confirmation { .. } => "confirmation",
+            Kind::MultiAction { .. } => "multi_action",
+            Kind::ServerLinks { .. } => "server_links",
+            Kind::DialogList { .. } => "dialog_list",
+        };
+        let inputs: Vec<Value> = self
+            .inputs
+            .iter()
+            .zip(values)
+            .map(|(i, v)| {
+                let kind = match i.control {
+                    Control::Text { .. } => "text",
+                    Control::Boolean { .. } => "boolean",
+                    Control::SingleOption { .. } => "single_option",
+                    Control::NumberRange { .. } => "number_range",
+                };
+                json!({"key": i.key, "type": kind, "value": i.control.substitution(v)})
+            })
+            .collect();
+        json!({
+            "type": kind,
+            "title": self.title.plain(),
+            "body": self.body.iter().map(|b| match b {
+                Body::Message { contents, .. } => contents.plain(),
+                Body::Item { item, .. } => string(item.get("id")).unwrap_or_default(),
+            }).collect::<Vec<_>>(),
+            "inputs": inputs,
+            "buttons": self.buttons().iter().map(|b| b.label.plain()).collect::<Vec<_>>(),
+            "can_close_with_escape": self.can_close_with_escape,
+            "after_action": match self.after_action {
+                AfterAction::Close => "close",
+                AfterAction::None => "none",
+                AfterAction::WaitForResponse => "wait_for_response",
+            },
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn s(v: &str) -> Tag {
+        Tag::String(v.into())
+    }
+
+    /// The register dialog AuthMe 6 sends in configuration (the shape its
+    /// `show_dialog` packet has on the test bed).
+    fn register() -> Tag {
+        Tag::compound([
+            ("type", s("minecraft:multi_action")),
+            ("title", s("Register")),
+            ("can_close_with_escape", Tag::Byte(0)),
+            ("after_action", s("wait_for_response")),
+            (
+                "body",
+                Tag::compound([
+                    ("type", s("minecraft:plain_message")),
+                    ("contents", s("Choose a password")),
+                ]),
+            ),
+            (
+                "inputs",
+                Tag::List(vec![Tag::compound([
+                    ("type", s("minecraft:text")),
+                    ("key", s("password")),
+                    ("label", s("Password")),
+                ])]),
+            ),
+            (
+                "actions",
+                Tag::List(vec![
+                    Tag::compound([
+                        ("label", s("Register")),
+                        (
+                            "action",
+                            Tag::compound([
+                                ("type", s("minecraft:dynamic/custom")),
+                                ("id", s("authme:prejoin-register/submit")),
+                            ]),
+                        ),
+                    ]),
+                    Tag::compound([
+                        ("label", s("Cancel")),
+                        (
+                            "action",
+                            Tag::compound([
+                                ("type", s("minecraft:dynamic/run_command")),
+                                ("template", s("say $(password) $(missing)!")),
+                            ]),
+                        ),
+                    ]),
+                ]),
+            ),
+        ])
+    }
+
+    #[test]
+    fn decodes_a_multi_action_dialog_with_defaults() {
+        let d = Dialog::parse(&register()).unwrap();
+        assert_eq!(d.title.plain(), "Register");
+        assert!(!d.can_close_with_escape);
+        assert!(d.pause);
+        assert_eq!(d.after_action, AfterAction::WaitForResponse);
+        assert!(matches!(&d.body[..], [Body::Message { width: 200, .. }]));
+        let Kind::MultiAction {
+            actions,
+            exit,
+            columns,
+        } = &d.kind
+        else {
+            panic!("{:?}", d.kind)
+        };
+        assert_eq!((actions.len(), exit.is_none(), *columns), (2, true, 2));
+        assert_eq!(actions[0].width, 150);
+        assert!(d.on_cancel().is_none());
+        let [
+            Input {
+                key,
+                control:
+                    Control::Text {
+                        max_length: 32,
+                        width: 200,
+                        ..
+                    },
+            },
+        ] = &d.inputs[..]
+        else {
+            panic!("{:?}", d.inputs)
+        };
+        assert_eq!(key, "password");
+    }
+
+    #[test]
+    fn actions_carry_the_input_values() {
+        let d = Dialog::parse(&register()).unwrap();
+        let values = [InputValue::Text("p\"w".into())];
+        let Kind::MultiAction { actions, .. } = &d.kind else {
+            unreachable!()
+        };
+        let custom = actions[0]
+            .action
+            .as_ref()
+            .unwrap()
+            .click(&d.inputs, &values);
+        assert_eq!(
+            custom,
+            Some(Click::Custom {
+                id: "authme:prejoin-register/submit".into(),
+                payload: Some(Tag::compound([("password", s("p\"w"))])),
+            })
+        );
+        // The template escapes the text; a key no input has becomes nothing.
+        let command = actions[1]
+            .action
+            .as_ref()
+            .unwrap()
+            .click(&d.inputs, &values);
+        assert_eq!(command, Some(Click::RunCommand("say p\\\"w !".into())));
+    }
+
+    #[test]
+    fn a_notice_without_an_action_has_ok() {
+        let d = Dialog::parse(&Tag::compound([("type", s("notice")), ("title", s("Hi"))])).unwrap();
+        let Kind::Notice(b) = &d.kind else {
+            unreachable!()
+        };
+        assert_eq!(b.label, Text::translate("gui.ok", &[]));
+        // Without a title, or with an unknown type, there is no dialog.
+        assert!(Dialog::parse(&Tag::compound([("type", s("notice"))])).is_none());
+        assert!(Dialog::parse(&Tag::compound([("type", s("x")), ("title", s("Hi"))])).is_none());
+    }
+
+    #[test]
+    fn number_ranges_snap_to_their_step() {
+        let mut range = Control::NumberRange {
+            width: 200,
+            label: Text::literal("n"),
+            label_format: "options.generic_value".into(),
+            start: 0.0,
+            end: 10.0,
+            initial: Some(4.0),
+            step: Some(3.0),
+        };
+        assert_eq!(range.initial(), InputValue::Slider(0.4));
+        assert_eq!(range.scaled(&InputValue::Slider(0.62)), Some(7.0));
+        assert_eq!(range.scaled(&InputValue::Slider(1.0)), Some(10.0));
+        let Control::NumberRange { step, .. } = &mut range else {
+            unreachable!()
+        };
+        *step = Some(4.0);
+        // 12 is out of range: one step less.
+        assert_eq!(range.scaled(&InputValue::Slider(1.0)), Some(8.0));
+        assert_eq!(range.substitution(&InputValue::Slider(0.0)), "0");
+        assert_eq!(number_string(2.5), "2.5");
+    }
+}
diff --git a/crates/horizon-client/src/dialog_screen.rs b/crates/horizon-client/src/dialog_screen.rs
new file mode 100644
index 000000000..c9434cfc2
--- /dev/null
+++ b/crates/horizon-client/src/dialog_screen.rs
@@ -0,0 +1,304 @@
+//! `DialogScreen` and its kinds (`SimpleDialogScreen`, `MultiButtonDialogScreen`):
+//! where a server dialog's title, body and buttons go in a
+//! `HeaderAndFooterLayout` (a 33 high header, the body in a `ScrollableLayout`,
+//! the footer), and the `WaitingForResponseScreen` an answer can leave open.
+use crate::{
+    dialog::{Body, Dialog, Kind},
+    font::Font,
+    text::Text,
+};
+
+/// `HeaderAndFooterLayout.DEFAULT_HEADER_AND_FOOTER_HEIGHT`.
+const BAR: f32 = 33.0;
+/// `DialogScreen.WARNING_BUTTON_SPRITES`: normal, disabled, highlighted.
+pub const WARNING_SPRITES: [&str; 3] = [
+    "gui/sprites/dialog/warning_button",
+    "gui/sprites/dialog/warning_button_disabled",
+    "gui/sprites/dialog/warning_button_highlighted",
+];
+
+/// One drawn piece; `y` is from the top of the body (before it scrolls) for
+/// the body's parts, from the top of the screen for the footer's.
+#[derive(Clone, Debug, PartialEq)]
+pub enum Part {
+    /// A line of text and where it starts.
+    Line(Text, f32, f32),
+    /// A button of `Dialog::buttons`.
+    Button { index: usize, rect: [f32; 4] },
+}
+
+#[derive(Clone, Debug)]
+pub struct Layout {
+    /// The title and where it is drawn.
+    pub title: (f32, f32),
+    pub warning: [f32; 4],
+    /// The body's visible area (`ScrollableLayout`'s container): x, y, w, h.
+    pub area: [f32; 4],
+    /// The body's full height: more than the area's scrolls.
+    pub content: f32,
+    pub body: Vec<Part>,
+    pub footer: Vec<Part>,
+}
+
+/// A laid-out element of a `LinearLayout` before it is placed.
+struct Element {
+    w: f32,
+    h: f32,
+    parts: Vec<Part>,
+}
+impl Element {
+    /// Its parts moved to `(x, y)`.
+    fn at(self, x: f32, y: f32) -> impl Iterator<Item = Part> {
+        self.parts.into_iter().map(move |p| match p {
+            Part::Line(t, px, py) => Part::Line(t, px + x, py + y),
+            Part::Button { index, rect } => Part::Button {
+                index,
+                rect: shift(rect, x, y),
+            },
+        })
+    }
+}
+fn shift([x, y, w, h]: [f32; 4], dx: f32, dy: f32) -> [f32; 4] {
+    [x + dx, y + dy, w, h]
+}
+/// `FrameLayout.alignInDimension` at 0.5: the offset that centres `inner`.
+fn centre(outer: f32, inner: f32) -> f32 {
+    ((outer - inner) * 0.5).trunc()
+}
+
+/// `FocusableTextWidget` with the body's settings: `width` wide, the text
+/// wrapped to `width - 8` and centred, 4 of padding all round.
+fn message(font: &Font, contents: &Text, width: f32) -> Element {
+    let lines = font.split_lines(contents, width - 8.0);
+    let mid = (width / 2.0).trunc();
+    let parts = lines
+        .into_iter()
+        .enumerate()
+        .map(|(i, (line, _))| {
+            let x = mid - (font.width_text(&line) / 2.0).trunc();
+            Part::Line(line, x, 4.0 + 9.0 * i as f32)
+        })
+        .collect::<Vec<_>>();
+    Element {
+        w: width,
+        h: 9.0 * parts.len() as f32 + 8.0,
+        parts,
+    }
+}
+
+/// `DialogScreen.packControlsIntoColumns`: full rows in a grid 2 apart, what
+/// is left in a centred row under them.
+fn columns(widths: &[f32], columns: usize, first: usize) -> Element {
+    let columns = columns.max(1);
+    let full = widths.len() / columns * columns;
+    let row_width = |ws: &[f32]| ws.iter().sum::<f32>() + 2.0 * (ws.len().max(1) - 1) as f32;
+    let mut col = vec![0.0f32; columns];
+    for (i, w) in widths[..full].iter().enumerate() {
+        col[i % columns] = col[i % columns].max(*w);
+    }
+    let last = &widths[full..];
+    if !last.is_empty() {
+        // GridLayout spreads a cell over every column it spans (Divisor).
+        let spread = row_width(last) - 2.0 * (columns - 1) as f32;
+        let (each, extra) = ((spread / columns as f32).floor(), spread % columns as f32);
+        for (c, w) in col.iter_mut().enumerate() {
+            *w = w.max(each + f32::from(u8::from((c as f32) < extra)));
+        }
+    }
+    let x_of = |c: usize| col[..c].iter().sum::<f32>() + 2.0 * c as f32;
+    let mut parts = Vec::new();
+    for (i, w) in widths[..full].iter().enumerate() {
+        let (r, c) = (i / columns, i % columns);
+        parts.push(Part::Button {
+            index: first + i,
+            rect: [x_of(c) + centre(col[c], *w), 22.0 * r as f32, *w, 20.0],
+        });
+    }
+    let width = x_of(columns - 1) + col[columns - 1];
+    if !last.is_empty() {
+        let y = 22.0 * (full / columns) as f32;
+        let mut x = centre(width, row_width(last));
+        for (i, w) in last.iter().enumerate() {
+            parts.push(Part::Button {
+                index: first + full + i,
+                rect: [x, y, *w, 20.0],
+            });
+            x += w + 2.0;
+        }
+    }
+    let rows = full / columns + usize::from(!last.is_empty());
+    Element {
+        w: width,
+        h: (22.0 * rows as f32 - 2.0).max(0.0),
+        parts,
+    }
+}
+
+impl Layout {
+    /// `DialogScreen.init` and `repositionElements` on a `w` by `h` screen.
+    pub fn new(dialog: &Dialog, font: &Font, (w, h): (f32, f32)) -> Self {
+        // The header: the title, 10 right of it the warning button, both
+        // centred together.
+        let tw = font.width_text(&dialog.title);
+        let (hx, hy) = (centre(w, tw + 30.0), centre(BAR, 20.0));
+        let title = (hx, hy + centre(20.0, 9.0));
+        let warning = [hx + tw + 10.0, hy, 20.0, 20.0];
+
+        let mut elements: Vec<Element> = dialog
+            .body
+            .iter()
+            .filter_map(|b| match b {
+                Body::Message { contents, width } => Some(message(font, contents, *width as f32)),
+                Body::Item { .. } => None,
+            })
+            .collect();
+        let buttons = dialog.buttons();
+        let (listed, footer_buttons, footer_h) = match &dialog.kind {
+            Kind::MultiAction {
+                actions,
+                exit,
+                columns: n,
+            } => {
+                let widths: Vec<f32> = actions.iter().map(|b| b.width as f32).collect();
+                elements.push(columns(&widths, *n as usize, 0));
+                // ButtonListDialogScreen: the exit button in the footer, else a 5 high one.
+                let footer = exit.as_ref().map(|_| actions.len()).into_iter().collect();
+                (
+                    actions.len(),
+                    footer,
+                    if exit.is_some() { BAR } else { 5.0 },
+                )
+            }
+            Kind::ServerLinks { exit, .. } | Kind::DialogList { exit, .. } => {
+                let footer = exit.as_ref().map(|_| 0).into_iter().collect();
+                (0, footer, if exit.is_some() { BAR } else { 5.0 })
+            }
+            // SimpleDialogScreen: the buttons side by side, 8 apart.
+            Kind::Notice(_) | Kind::Confirmation { .. } => {
+                (0, (0..buttons.len()).collect::<Vec<_>>(), BAR)
+            }
+        };
+        debug_assert!(listed + footer_buttons.len() <= buttons.len());
+
+        // The body: a column 10 apart, each element centred in it.
+        let body_w = elements.iter().map(|e| e.w).fold(0.0, f32::max);
+        let content = elements.iter().map(|e| e.h).sum::<f32>()
+            + 10.0 * elements.len().saturating_sub(1) as f32;
+        // ScrollableLayout: 10 each side for the scrollbar (ReserveStrategy.BOTH),
+        // no higher than what the header and footer leave.
+        let area_w = body_w + 20.0;
+        let area_h = content.min(h - BAR - footer_h).max(0.0);
+        let area_y = (BAR + 30.0).min(h - footer_h - area_h);
+        let area_x = centre(w, area_w);
+        let mut body = Vec::new();
+        let mut y = 0.0;
+        for e in elements {
+            let (x, eh) = (area_x + 10.0 + centre(body_w, e.w), e.h);
+            body.extend(e.at(x, y));
+            y += eh + 10.0;
+        }
+
+        let widths: Vec<f32> = footer_buttons
+            .iter()
+            .map(|&i| buttons[i].width as f32)
+            .collect();
+        let row = widths.iter().sum::<f32>() + 8.0 * widths.len().saturating_sub(1) as f32;
+        let (mut x, fy) = (centre(w, row), h - footer_h + centre(footer_h, 20.0));
+        let mut footer = Vec::new();
+        for (&i, bw) in footer_buttons.iter().zip(&widths) {
+            footer.push(Part::Button {
+                index: i,
+                rect: [x, fy, *bw, 20.0],
+            });
+            x += bw + 8.0;
+        }
+        Self {
+            title,
+            warning: Self::in_bounds(warning, w, h),
+            area: [area_x, area_y, area_w, area_h],
+            content,
+            body,
+            footer,
+        }
+    }
+    /// `makeSureWarningButtonIsInBounds`.
+    fn in_bounds(r: [f32; 4], w: f32, h: f32) -> [f32; 4] {
+        if r[0] < 0.0 || r[1] < 0.0 || r[0] > w - 20.0 || r[1] > h - 20.0 {
+            [(w - 40.0).max(0.0), 5.0f32.min(h), 20.0, 20.0]
+        } else {
+            r
+        }
+    }
+    /// Every part where it is drawn with the body scrolled by `scroll`, and
+    /// whether it is in the body (clipped to its area).
+    pub fn placed(&self, scroll: f32) -> impl Iterator<Item = (Part, bool)> + '_ {
+        let dy = self.area[1] - scroll;
+        let body = self.body.iter().map(move |p| {
+            let p = match p.clone() {
+                Part::Line(t, x, y) => Part::Line(t, x, y + dy),
+                Part::Button { index, rect } => Part::Button {
+                    index,
+                    rect: shift(rect, 0.0, dy),
+                },
+            };
+            (p, true)
+        });
+        body.chain(self.footer.iter().map(|p| (p.clone(), false)))
+    }
+}
+
+/// `WaitingForResponseScreen`: its Back button's label after `ticks`, and
+/// whether it shows and works (it shows after a second, works after five).
+pub fn waiting_button(ticks: u32) -> (Text, bool, bool) {
+    let seconds = (ticks / 20).min(5);
+    let label = match seconds {
+        0 => Text::literal(""),
+        5 => Text::translate("gui.back", &[]),
+        s => Text::translate(
+            "gui.waitingForResponse.button.inactive",
+            &[Text::literal((5 - s).to_string())],
+        ),
+    };
+    (label, seconds >= 1, seconds == 5)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn grids_pack_full_rows_and_centre_the_rest() {
+        // AuthMe's two buttons: one row, 2 apart.
+        let two = columns(&[150.0, 150.0], 2, 0);
+        assert_eq!((two.w, two.h), (302.0, 20.0));
+        // Three in two columns: the third alone, centred under them.
+        let three = columns(&[150.0, 150.0, 150.0], 2, 0);
+        assert_eq!((three.w, three.h), (302.0, 42.0));
+        assert_eq!(
+            three.parts[2],
+            Part::Button {
+                index: 2,
+                rect: [76.0, 22.0, 150.0, 20.0]
+            }
+        );
+        // One in two columns spreads over both.
+        let one = columns(&[100.0], 2, 0);
+        assert_eq!(one.w, 100.0);
+    }
+
+    #[test]
+    fn the_waiting_screens_button_counts_down() {
+        assert!(!waiting_button(0).1);
+        assert_eq!(
+            waiting_button(20).0,
+            Text::translate(
+                "gui.waitingForResponse.button.inactive",
+                &[Text::literal("4")]
+            )
+        );
+        assert_eq!(
+            waiting_button(100),
+            (Text::translate("gui.back", &[]), true, true)
+        );
+    }
+}
diff --git a/crates/horizon-client/src/game.rs b/crates/horizon-client/src/game.rs
index 942e8699f..4ae9364f3 100644
--- a/crates/horizon-client/src/game.rs
+++ b/crates/horizon-client/src/game.rs
@@ -37,6 +37,7 @@ mod debug_keys;
 mod decorated_pot;
 mod dedicated;
 mod deflect;
+mod dialogs;
 mod discord;
 mod dispense_fixture;
 mod dispenser;
@@ -1145,6 +1146,7 @@ struct Game<'a> {
     pending_pack_reload: bool,
     /// A server's resource packs (game/server_packs.rs).
     server_packs: server_packs::ServerPackState,
+    dialogs: dialogs::DialogState,
     world_renderer_ready: bool,
     collision: &'a BlockCollisionRegistry<'a>,
     motion: &'a MotionResources,
@@ -4841,11 +4843,14 @@ impl Game<'_> {
     fn hud(&mut self, size: [u32; 2]) -> HudBatch {
         // The pack prompt replaces the connecting screen (setScreen), but
         // in game it opens over the world.
-        let mut batch = if self.server_packs.prompt.is_some() && self.player.is_none() {
+        let mut batch = if (self.server_packs.prompt.is_some() || self.dialog_open())
+            && self.player.is_none()
+        {
             HudBatch::new(size)
         } else {
             self.hud_layers(size)
         };
+        self.draw_dialog(&mut batch);
         self.draw_pack_prompt(&mut batch);
         // Gui.extractRenderState: the debug overlay comes after the screen
         // and the toasts, so it is over everything, menus included.
@@ -10435,6 +10440,7 @@ impl Game<'_> {
             || (self.title.is_none()
                 && self.player.is_some()
                 && (self.screen.blurs_background(self.pause_menu)
+                    || self.dialog_open()
                     || (self.screen == Screen::Win && self.win_screen_pauses())));
         let radius = self.settings.menu_blur as f32;
         (blurred && radius >= 1.0).then_some(radius)
@@ -11137,7 +11143,9 @@ impl ApplicationHandler for Game<'_> {
                         }) * wheel_sensitivity
                     };
                     let d = scaled(raw_y) as f32;
-                    if let Some(title) = &mut self.title
+                    if self.dialog_open() {
+                        self.dialog_scroll(d);
+                    } else if let Some(title) = &mut self.title
                         && self.screen != Screen::Win
                     {
                         let size = self
@@ -11207,6 +11215,11 @@ impl ApplicationHandler for Game<'_> {
                         self.pack_prompt_click()?;
                     }
                 }
+                WindowEvent::MouseInput { state, button, .. } if self.dialog_open() => {
+                    if state == ElementState::Pressed && button == MouseButton::Left {
+                        self.dialog_click()?;
+                    }
+                }
                 WindowEvent::MouseInput { .. } if self.screen == Screen::Win => {}
                 WindowEvent::MouseInput { state, button, .. } if self.screen == Screen::Options => {
                     if self.options_waiting_for_key() && state == ElementState::Pressed {
@@ -11421,6 +11434,13 @@ impl ApplicationHandler for Game<'_> {
                         self.answer_pack_prompt(false)?;
                     }
                 }
+                WindowEvent::KeyboardInput { event, .. } if self.dialog_open() => {
+                    if event.state == ElementState::Pressed
+                        && let PhysicalKey::Code(key) = event.physical_key
+                    {
+                        self.dialog_key(key)?
+                    }
+                }
                 WindowEvent::KeyboardInput { event, .. }
                     if self.screen == Screen::Chat && self.title.is_none() =>
                 {
@@ -11902,6 +11922,7 @@ impl<'a> Game<'a> {
             world_loader: None,
             pending_pack_reload: false,
             server_packs: Default::default(),
+            dialogs: Default::default(),
             world_renderer_ready: false,
             collision: res.collision(),
             motion: res.motion(),
diff --git a/crates/horizon-client/src/game/agent.rs b/crates/horizon-client/src/game/agent.rs
index 0d2d218ab..27e00e391 100644
--- a/crates/horizon-client/src/game/agent.rs
+++ b/crates/horizon-client/src/game/agent.rs
@@ -390,6 +390,9 @@ impl Game<'_> {
         Ok(())
     }
     pub(super) fn screen_label(&self) -> &'static str {
+        if self.dialog_open() {
+            return "dialog";
+        }
         if self.title.is_some() {
             return "title";
         }
@@ -485,6 +488,7 @@ impl Game<'_> {
             })
         });
         json!({
+            "dialog": self.dialog_status(),
             "screen": self.screen_label(),
             "menu": self.title.as_ref().map(|_| self.title_value()),
             "world": (self.title.is_none()).then(|| match &self.integrated {
diff --git a/crates/horizon-client/src/game/control.rs b/crates/horizon-client/src/game/control.rs
index d0a139850..182bcd516 100644
--- a/crates/horizon-client/src/game/control.rs
+++ b/crates/horizon-client/src/game/control.rs
@@ -241,6 +241,13 @@ impl Game<'_> {
             "pad" => Ok(Some(self.pad_command(&words)?)),
             "key" => {
                 let key = key_code(arg(1)?).ok_or_else(|| format!("unknown key {}", words[1]))?;
+                // A server's dialog takes the keys, in configuration too.
+                if self.dialog_open() {
+                    if arg(2)? != "up" {
+                        self.dialog_key(key)?;
+                    }
+                    return ok();
+                }
                 self.require_world()?;
                 // The sign editor takes raw presses (Enter, arrows, Backspace, Escape).
                 if self.sign_edit.is_some() {
diff --git a/crates/horizon-client/src/game/dialogs.rs b/crates/horizon-client/src/game/dialogs.rs
new file mode 100644
index 000000000..28a7a7609
--- /dev/null
+++ b/crates/horizon-client/src/game/dialogs.rs
@@ -0,0 +1,450 @@
+//! A server's dialogs bound to the game (`ClientCommonPacketListenerImpl.
+//! showDialog` and `clearDialog`, `DialogScreen`, its `WarningScreen` and the
+//! `WaitingForResponseScreen`): the screen over whatever is open (the
+//! connecting screen in configuration), its inputs, and the actions its
+//! buttons send back.
+use super::Game;
+use horizon_client::{
+    Result,
+    confirm_screen::Confirm,
+    dialog::{AfterAction, Click, Dialog, InputValue},
+    dialog_screen::{Layout, Part, WARNING_SPRITES, waiting_button},
+    hud::{HudBatch, rgba},
+    text::Text,
+    ui,
+};
+use horizon_world::nbt::Tag;
+use std::time::Instant;
+use winit::keyboard::KeyCode;
+
+/// An open `DialogScreen`.
+struct Open {
+    dialog: Dialog,
+    values: Vec<InputValue>,
+    scroll: ui::Scroll,
+}
+
+/// The dialog screens a server can open.
+#[derive(Default)]
+pub(super) struct DialogState {
+    open: Option<Open>,
+    /// `WaitingForResponseScreen`, since when.
+    waiting: Option<Instant>,
+    /// `DialogScreen.WarningScreen`, over the dialog.
+    warning: bool,
+}
+
+fn warning_texts() -> (Text, Text, [Text; 2]) {
+    let t = |key: &str| Text::translate(key, &[]);
+    (
+        t("menu.custom_screen_info.title"),
+        t("menu.custom_screen_info.contents"),
+        [t("menu.disconnect"), t("gui.back")],
+    )
+}
+
+impl Game<'_> {
+    /// Whether a dialog screen takes the input.
+    pub(super) fn dialog_open(&self) -> bool {
+        let d = &self.dialogs;
+        d.open.is_some() || d.waiting.is_some() || d.warning
+    }
+
+    /// `showDialog`: the dialog replaces an open one (and a waiting screen);
+    /// under the warning screen, it is what Back returns to.
+    pub(super) fn show_dialog(&mut self, tag: &Tag) {
+        let Some(dialog) = Dialog::parse(tag) else {
+            log::warn!("Horizon: failed to show dialog for data {tag:?}");
+            return;
+        };
+        let values = dialog.inputs.iter().map(|i| i.control.initial()).collect();
+        self.dialogs.open = Some(Open {
+            dialog,
+            values,
+            scroll: ui::Scroll::default(),
+        });
+        self.dialogs.waiting = None;
+        self.capture(false);
+    }
+
+    /// `clearDialog`: the dialog closes (under the warning screen, Back then
+    /// returns to what was open before it).
+    pub(super) fn clear_dialog(&mut self) {
+        if self.dialogs.open.take().is_some() && !self.dialog_open() {
+            self.dialog_closed();
+        }
+    }
+
+    /// Every dialog screen goes (a disconnect, or the level loading screen).
+    pub(super) fn close_dialogs(&mut self) {
+        self.dialogs = DialogState::default();
+    }
+
+    fn dialog_closed(&mut self) {
+        if self.player.is_some() && self.screen == super::Screen::Playing && self.title.is_none() {
+            self.capture(true);
+        }
+    }
+
+    /// `DialogScreen.runAction`: the click event, then the screen the dialog's
+    /// `after_action` leaves.
+    fn run_dialog_action(&mut self, click: Option<Click>, after: AfterAction) -> Result<()> {
+        match after {
+            AfterAction::None => {}
+            AfterAction::Close => self.dialogs.open = None,
+            AfterAction::WaitForResponse => {
+                self.dialogs.open = None;
+                self.dialogs.waiting = Some(Instant::now());
+            }
+        }
+        match click {
+            Some(Click::Custom { id, payload }) => {
+                if let Some(r) = &self.remote {
+                    r.session.send_custom_click(&id, payload);
+                }
+            }
+            Some(Click::RunCommand(command)) => {
+                // In configuration there is nothing to run it (vanilla warns).
+                if self.player.is_some() {
+                    let command = command.strip_prefix('/').unwrap_or(&command);
+                    self.send_chat(&format!("/{command}"));
+                } else {
+                    log::warn!(
+                        "Horizon: commands are not supported in configuration, trying to run '{command}'"
+                    );
+                }
+            }
+            Some(Click::ShowDialog(dialog)) => self.show_dialog_ref(&dialog),
+            Some(Click::CopyToClipboard(value)) => {
+                use horizon_client::clipboard::Clipboard;
+                self.clipboard.set(&value);
+            }
+            Some(other) => log::info!("Horizon: dialog action {other:?} is not supported yet"),
+            None => {}
+        }
+        if !self.dialog_open() {
+            self.dialog_closed();
+        }
+        Ok(())
+    }
+
+    /// A `show_dialog` click event's dialog: a registry id or the dialog itself.
+    fn show_dialog_ref(&mut self, dialog: &Tag) {
+        match dialog {
+            Tag::String(id) => {
+                let id = id.to_string_lossy();
+                let name = if id.contains(':') {
+                    id.clone()
+                } else {
+                    format!("minecraft:{id}")
+                };
+                let found = self.remote.as_ref().and_then(|r| {
+                    let entries = r.registries.registries.get("minecraft:dialog")?;
+                    entries.iter().find(|(n, _)| *n == name)?.1.clone()
+                });
+                match found {
+                    Some(tag) => self.show_dialog(&tag),
+                    None => log::warn!("Horizon: unknown dialog {id}"),
+                }
+            }
+            tag => self.show_dialog(tag),
+        }
+    }
+
+    /// `ClientboundShowDialogPacket` in play: a registry entry or the dialog.
+    pub(super) fn show_play_dialog(
+        &mut self,
+        dialog: &horizon_protocol::packets::play::DialogHolder,
+    ) {
+        use horizon_protocol::packets::play::DialogHolder;
+        match dialog {
+            DialogHolder::Direct(tag) => self.show_dialog(tag),
+            DialogHolder::Registry(id) => {
+                let tag = self
+                    .remote
+                    .as_ref()
+                    .and_then(|r| r.registries.data("minecraft:dialog", *id).cloned());
+                match tag {
+                    Some(tag) => self.show_dialog(&tag),
+                    None => log::warn!("Horizon: unknown dialog {id}"),
+                }
+            }
+        }
+    }
+
+    fn dialog_layout(&self) -> Option<Layout> {
+        let open = self.dialogs.open.as_ref()?;
+        Some(Layout::new(
+            &open.dialog,
+            &self.gui.atlas.font,
+            self.gui_size(),
+        ))
+    }
+
+    pub(super) fn draw_dialog(&mut self, batch: &mut HudBatch) {
+        if !self.dialog_open() {
+            return;
+        }
+        let (w, h) = (batch.width, batch.height);
+        let cursor = self.cursor;
+        let atlas = &self.gui.atlas;
+        if self.player.is_none() {
+            // In place of the connecting screen, on its background.
+            batch.fill(atlas, 0.0, 0.0, w, h, rgba(20, 20, 20, 255));
+        }
+        ui::menu_background(batch, atlas, 0.0, 0.0, w, h, self.player.is_some());
+        if self.dialogs.warning {
+            let (title, message, [disconnect, back]) = warning_texts();
+            Confirm::new(&atlas.font, (w, h), &title, &message).draw(
+                batch,
+                atlas,
+                cursor,
+                [&disconnect, &back],
+            );
+            return;
+        }
+        if let Some(since) = self.dialogs.waiting {
+            // HeaderAndFooterLayout(33, 0) centred: the title, the button 33 below.
+            let ticks = (since.elapsed().as_millis() / 50) as u32;
+            let (label, visible, active) = waiting_button(ticks);
+            let title = Text::translate("gui.waitingForResponse.title", &[]);
+            let top = ((h - 53.0) / 2.0).trunc();
+            let tw = atlas.font.width_text(&title);
+            batch.text_styled(
+                atlas,
+                &title,
+                ((w - tw) / 2.0).trunc(),
+                top + 12.0,
+                u32::MAX,
+                true,
+            );
+            if visible {
+                let (bx, by) = (((w - 200.0) / 2.0).trunc(), top + 33.0);
+                let hover = ui::hovered(cursor, bx, by, 200.0, 20.0);
+                ui::button(batch, atlas, bx, by, 200.0, 20.0, &label, active, hover);
+            }
+            return;
+        }
+        let Some(layout) = self.dialog_layout() else {
+            return;
+        };
+        let Some(open) = self.dialogs.open.as_mut() else {
+            return;
+        };
+        let atlas = &self.gui.atlas;
+        let [ax, ay, aw, ah] = layout.area;
+        open.scroll.clamp(ay, ay + ah, layout.content);
+        batch.text_styled(
+            atlas,
+            &open.dialog.title,
+            layout.title.0,
+            layout.title.1,
+            u32::MAX,
+            true,
+        );
+        let [wx, wy, ww, wh] = layout.warning;
+        let warn_hover = ui::hovered(cursor, wx, wy, ww, wh);
+        horizon_client::widgets::record("warning", layout.warning, true);
+        batch.sprite_scaled(
+            atlas,
+            WARNING_SPRITES[if warn_hover { 2 } else { 0 }],
+            wx,
+            wy,
+            ww,
+            wh,
+            u32::MAX,
+        );
+        let buttons = open.dialog.buttons();
+        let in_area = |y: f32| y >= ay && y < ay + ah;
+        let mut tooltip = None;
+        let mut start = None;
+        for (part, clipped) in layout.placed(open.scroll.amount) {
+            if clipped && start.is_none() {
+                start = Some(batch.vertices.len());
+            } else if !clipped && let Some(s) = start.take() {
+                batch.clip_since(s, ax, ay, ax + aw, ay + ah);
+            }
+            match part {
+                Part::Line(text, x, y) => {
+                    batch.text_styled(atlas, &text, x, y, u32::MAX, true);
+                }
+                Part::Button { index, rect } => {
+                    let [x, y, bw, bh] = rect;
+                    let hover =
+                        (!clipped || in_area(cursor.1)) && ui::hovered(cursor, x, y, bw, bh);
+                    let b = buttons[index];
+                    ui::button(batch, atlas, x, y, bw, bh, &b.label, true, hover);
+                    if hover && let Some(t) = &b.tooltip {
+                        tooltip = Some(t.clone());
+                    }
+                }
+            }
+        }
+        if let Some(s) = start {
+            batch.clip_since(s, ax, ay, ax + aw, ay + ah);
+        }
+        if layout.content > ah {
+            ui::scrollbar(
+                batch,
+                atlas,
+                ax + aw - 6.0,
+                ay,
+                ay + ah,
+                layout.content,
+                open.scroll.amount,
+            );
+        }
+        if warn_hover {
+            tooltip = Some(Text::translate("menu.custom_screen_info.tooltip", &[]));
+        }
+        if let Some(t) = tooltip {
+            let lines: Vec<Text> = atlas
+                .font
+                .split_lines(&t, 170.0)
+                .into_iter()
+                .map(|l| l.0)
+                .collect();
+            ui::tooltip(batch, atlas, &lines, cursor);
+        }
+    }
+
+    /// A left click on a dialog screen.
+    pub(super) fn dialog_click(&mut self) -> Result<()> {
+        let cursor = self.cursor;
+        if self.dialogs.warning {
+            let (title, message, _) = warning_texts();
+            let answer = Confirm::new(&self.gui.atlas.font, self.gui_size(), &title, &message)
+                .answer_at(cursor);
+            match answer {
+                Some(true) => {
+                    self.audio.play_button_click();
+                    let reason = Text::translate("menu.custom_screen_info.disconnect", &[]);
+                    return self.leave_server(Some(reason.plain()));
+                }
+                Some(false) => {
+                    self.audio.play_button_click();
+                    self.dialogs.warning = false;
+                    if !self.dialog_open() {
+                        self.dialog_closed();
+                    }
+                }
+                None => {}
+            }
+            return Ok(());
+        }
+        if let Some(since) = self.dialogs.waiting {
+            let (w, h) = self.gui_size();
+            let active = waiting_button((since.elapsed().as_millis() / 50) as u32).2;
+            let (bx, by) = (
+                ((w - 200.0) / 2.0).trunc(),
+                ((h - 53.0) / 2.0).trunc() + 33.0,
+            );
+            if active && ui::hovered(cursor, bx, by, 200.0, 20.0) {
+                self.audio.play_button_click();
+                self.dialogs.waiting = None;
+                self.dialog_closed();
+            }
+            return Ok(());
+        }
+        let Some(layout) = self.dialog_layout() else {
+            return Ok(());
+        };
+        let [wx, wy, ww, wh] = layout.warning;
+        if ui::hovered(cursor, wx, wy, ww, wh) {
+            self.audio.play_button_click();
+            self.dialogs.warning = true;
+            return Ok(());
+        }
+        let Some(open) = self.dialogs.open.as_mut() else {
+            return Ok(());
+        };
+        let [_, ay, _, ah] = layout.area;
+        let mut action = None;
+        for (part, clipped) in layout.placed(open.scroll.amount) {
+            if clipped && !(cursor.1 >= ay && cursor.1 < ay + ah) {
+                continue;
+            }
+            match part {
+                Part::Button {
+                    index,
+                    rect: [x, y, w, h],
+                } if ui::hovered(cursor, x, y, w, h) => {
+                    action = Some(index);
+                }
+                _ => {}
+            }
+        }
+        let Some(index) = action else {
+            return Ok(());
+        };
+        self.audio.play_button_click();
+        let d = &open.dialog;
+        let click = d.buttons()[index]
+            .action
+            .as_ref()
+            .and_then(|a| a.click(&d.inputs, &open.values));
+        let after = d.after_action;
+        self.run_dialog_action(click, after)
+    }
+
+    /// The mouse wheel over a dialog: its body scrolls 10 a step.
+    pub(super) fn dialog_scroll(&mut self, delta: f32) {
+        let Some(layout) = self.dialog_layout() else {
+            return;
+        };
+        if let Some(open) = self.dialogs.open.as_mut() {
+            let [_, ay, _, ah] = layout.area;
+            open.scroll.wheel(delta, 10.0, ay, ay + ah, layout.content);
+        }
+    }
+
+    /// A key pressed on a dialog screen: Escape closes what allows it.
+    pub(super) fn dialog_key(&mut self, key: KeyCode) -> Result<()> {
+        let escape = key == KeyCode::Escape;
+        if self.dialogs.warning {
+            if escape {
+                self.dialogs.warning = false;
+                if !self.dialog_open() {
+                    self.dialog_closed();
+                }
+            }
+            return Ok(());
+        }
+        if let Some(since) = self.dialogs.waiting {
+            // shouldCloseOnEsc: once Back works.
+            if escape && waiting_button((since.elapsed().as_millis() / 50) as u32).2 {
+                self.dialogs.waiting = None;
+                self.dialog_closed();
+            }
+            return Ok(());
+        }
+        let Some(open) = self.dialogs.open.as_ref() else {
+            return Ok(());
+        };
+        if escape {
+            if !open.dialog.can_close_with_escape {
+                return Ok(());
+            }
+            // onClose: the cancel action, and the screen closes.
+            let d = &open.dialog;
+            let click = d.on_cancel().and_then(|a| a.click(&d.inputs, &open.values));
+            return self.run_dialog_action(click, AfterAction::Close);
+        }
+        Ok(())
+    }
+
+    /// What `state` reports: the open dialog and its values, or the waiting
+    /// and warning screens.
+    pub(super) fn dialog_status(&self) -> serde_json::Value {
+        let d = &self.dialogs;
+        let screen = if d.warning {
+            Some("warning")
+        } else if d.waiting.is_some() {
+            Some("waiting_for_response")
+        } else {
+            None
+        };
+        let open = d.open.as_ref().map(|open| open.dialog.json(&open.values));
+        serde_json::json!({ "open": open, "screen": screen })
+    }
+}
diff --git a/crates/horizon-client/src/game/remote.rs b/crates/horizon-client/src/game/remote.rs
index 2d5ee9dc1..570eb6098 100644
--- a/crates/horizon-client/src/game/remote.rs
+++ b/crates/horizon-client/src/game/remote.rs
@@ -489,6 +489,7 @@ impl Game<'_> {
             r.session.disconnect();
         }
         self.server_packs_disconnect();
+        self.close_dialogs();
         // Single player's server thread saves the world before the title shows.
         let single_player = match self.integrated.take() {
             Some(server) => {
@@ -736,6 +737,8 @@ impl Game<'_> {
                 } => {
                     self.set_registries(registries);
                     self.extras_joined();
+                    // handleLogin: the level loading screen replaces any dialog.
+                    self.close_dialogs();
                     if let Some(r) = self.remote.as_mut() {
                         r.joined = true;
                         r.profile = uuid;
@@ -764,6 +767,8 @@ impl Game<'_> {
                 }
                 Event::PackPush(p) => self.handle_pack_push(p),
                 Event::PackPop(id) => self.handle_pack_pop(id),
+                Event::ShowDialog(dialog) => self.show_dialog(&dialog),
+                Event::ClearDialog => self.clear_dialog(),
                 Event::DecodeError(e) => {
                     if let Some(r) = self.remote.as_mut() {
                         r.decode_errors += 1;
@@ -2614,6 +2619,9 @@ impl Game<'_> {
             C::SetTitleText(p) => self.titles.set_title(remote_text(&p.text)),
             C::SetSubtitleText(p) => self.titles.set_subtitle(remote_text(&p.text)),
             C::SetTitlesAnimation(p) => self.titles.set_times(p.fade_in, p.stay, p.fade_out),
+            // ClientCommonPacketListenerImpl.handleShowDialog / handleClearDialog.
+            C::ShowDialog(p) => self.show_play_dialog(&p.dialog),
+            C::ClearDialog(_) => self.clear_dialog(),
             C::ClearTitles(p) => {
                 self.titles.clear();
                 if p.value {
diff --git a/crates/horizon-client/src/lib.rs b/crates/horizon-client/src/lib.rs
index bfb510c31..6f921d939 100644
--- a/crates/horizon-client/src/lib.rs
+++ b/crates/horizon-client/src/lib.rs
@@ -54,6 +54,8 @@ pub mod datapack;
 pub mod debug_chart;
 pub mod debug_keys;
 pub mod debug_overlay;
+pub mod dialog;
+pub mod dialog_screen;
 pub mod discord_presence;
 pub mod dynamic_light;
 pub mod effects;
diff --git a/crates/horizon-client/src/net.rs b/crates/horizon-client/src/net.rs
index 1986c5b1d..0eb260477 100644
--- a/crates/horizon-client/src/net.rs
+++ b/crates/horizon-client/src/net.rs
@@ -55,6 +55,10 @@ pub enum Event {
     PackPush(cfg::ResourcePackPush),
     /// ClientboundResourcePackPopPacket: one pack, or every pack.
     PackPop(Option<u128>),
+    /// `show_dialog` in configuration: the dialog itself.
+    ShowDialog(horizon_world::nbt::Tag),
+    /// `clear_dialog` in configuration.
+    ClearDialog,
     /// `ClientboundTransferPacket`: the server sent us to another address.
     /// The connection ends right after; the game reconnects there with the
     /// stored cookies.
@@ -234,6 +238,25 @@ impl Session {
             w.shutdown();
         }
     }
+    /// ServerboundCustomClickActionPacket (a dialog's answer), in whichever
+    /// phase the connection is.
+    pub fn send_custom_click(&self, id: &str, payload: Option<horizon_world::nbt::Tag>) {
+        let click = cfg::CustomClickAction {
+            id: id.to_owned(),
+            payload,
+        };
+        let mut writer = self.writer.lock().unwrap();
+        let body = if self.configuring.load(Ordering::Relaxed) {
+            cfg::Serverbound::CustomClickAction(click).encode()
+        } else {
+            play::Serverbound::CustomClickAction(click).encode()
+        };
+        if let Some(w) = writer.as_mut()
+            && w.send(&body).is_err()
+        {
+            w.shutdown();
+        }
+    }
     pub fn disconnect(&mut self) {
         if let Some(w) = self.writer.lock().unwrap().take() {
             w.shutdown();
@@ -602,6 +625,13 @@ fn configure(
             cfg::Clientbound::ResourcePackPop(p) => {
                 let _ = send.send(Event::PackPop(p.id));
             }
+            // The game shows it; the answer goes back from there.
+            cfg::Clientbound::ShowDialog(d) => {
+                let _ = send.send(Event::ShowDialog(d.dialog));
+            }
+            cfg::Clientbound::ClearDialog(_) => {
+                let _ = send.send(Event::ClearDialog);
+            }
             cfg::Clientbound::CookieRequest(q) => {
                 let payload = cookies.lock().unwrap().get(&q.key).cloned();
                 reply(cfg::Serverbound::CookieResponse(cfg::CookieResponse {
diff --git a/crates/horizon-protocol/src/packets/configuration.rs b/crates/horizon-protocol/src/packets/configuration.rs
index a767110eb..ced56dacf 100644
--- a/crates/horizon-protocol/src/packets/configuration.rs
+++ b/crates/horizon-protocol/src/packets/configuration.rs
@@ -45,6 +45,32 @@ packet!(
 packet!(KnownPack { namespace: String => Str, id: String => Str, version: String => Str });
 packet!(SelectKnownPacks { packs: Vec<KnownPack> => List<KnownPack> });
 packet!(CodeOfConduct { text: String => Str });
+packet!(
+    /// ClientboundShowDialogPacket.CONTEXT_FREE_STREAM_CODEC: the dialog
+    /// itself (`Dialog.DIRECT_CODEC` as NBT).
+    ShowDialog { dialog: Tag => Nbt }
+);
+packet!(
+    /// ServerboundCustomClickActionPacket: a `custom` click event's id and
+    /// payload (a dialog's answer).
+    CustomClickAction { id: String => Ident, payload: Option<Tag> => ClickPayload }
+);
+/// ServerboundCustomClickActionPacket.UNTRUSTED_TAG_CODEC: an optional tag
+/// (`End` when there is none) behind its length, 65536 bytes at most.
+pub struct ClickPayload;
+impl Codec<Option<Tag>> for ClickPayload {
+    fn read(r: &mut Reader) -> Result<Option<Tag>> {
+        let n = r.count(65536)?;
+        let tag = Reader::new(r.bytes(n)?).nbt()?;
+        Ok((tag != Tag::End).then_some(tag))
+    }
+    fn write(v: &Option<Tag>, w: &mut Writer) {
+        let mut tag = Writer::new();
+        tag.nbt(v.as_ref().unwrap_or(&Tag::End));
+        w.varint(tag.data.len() as i32);
+        w.bytes(&tag.data);
+    }
+}
 
 packet_enum!(Clientbound, crate::ids::configuration::clientbound {
     CookieRequest(CookieRequest) = COOKIE_REQUEST,
@@ -63,6 +89,7 @@ packet_enum!(Clientbound, crate::ids::configuration::clientbound {
     UpdateTags(UpdateTags) = UPDATE_TAGS,
     SelectKnownPacks(SelectKnownPacks) = SELECT_KNOWN_PACKS,
     ClearDialog(Empty) = CLEAR_DIALOG,
+    ShowDialog(ShowDialog) = SHOW_DIALOG,
     CodeOfConduct(CodeOfConduct) = CODE_OF_CONDUCT,
 });
 
@@ -142,6 +169,7 @@ packet_enum!(Serverbound, crate::ids::configuration::serverbound {
     ResourcePack(ResourcePackResponse) = RESOURCE_PACK,
     SelectKnownPacks(SelectKnownPacks) = SELECT_KNOWN_PACKS,
     AcceptCodeOfConduct(Empty) = ACCEPT_CODE_OF_CONDUCT,
+    CustomClickAction(CustomClickAction) = CUSTOM_CLICK_ACTION,
 });
 
 #[cfg(test)]
@@ -208,6 +236,10 @@ mod tests {
             Clientbound::CodeOfConduct(CodeOfConduct {
                 text: "Be nice".into(),
             }),
+            Clientbound::ShowDialog(ShowDialog {
+                dialog: Tag::compound([("type", Tag::String("minecraft:notice".into()))]),
+            }),
+            Clientbound::ClearDialog(Empty),
         ] {
             round_trip(p, Clientbound::encode, Clientbound::decode);
         }
@@ -219,8 +251,28 @@ mod tests {
             Serverbound::ResourcePack(ResourcePackResponse { id: 5, action: 1 }),
             Serverbound::SelectKnownPacks(SelectKnownPacks { packs: vec![] }),
             Serverbound::AcceptCodeOfConduct(Empty),
+            Serverbound::CustomClickAction(CustomClickAction {
+                id: "authme:prejoin-register/submit".into(),
+                payload: Some(Tag::compound([("password", Tag::String("hunter2".into()))])),
+            }),
+            Serverbound::CustomClickAction(CustomClickAction {
+                id: "minecraft:x".into(),
+                payload: None,
+            }),
         ] {
             round_trip(p, Serverbound::encode, Serverbound::decode);
         }
     }
+
+    /// The bytes vanilla writes: the length, then the tag (a lone `End` byte
+    /// for none).
+    #[test]
+    fn click_payload_is_length_prefixed() {
+        let mut w = Writer::new();
+        ClickPayload::write(&None, &mut w);
+        assert_eq!(w.data, [1, 0]);
+        let mut w = Writer::new();
+        ClickPayload::write(&Some(Tag::Byte(1)), &mut w);
+        assert_eq!(w.data, [2, 1, 1]);
+    }
 }
diff --git a/crates/horizon-protocol/src/packets/play.rs b/crates/horizon-protocol/src/packets/play.rs
index 67373cf4b..4f41fe0aa 100644
--- a/crates/horizon-protocol/src/packets/play.rs
+++ b/crates/horizon-protocol/src/packets/play.rs
@@ -13,9 +13,9 @@ use crate::{
     packets::{
         Empty,
         configuration::{
-            ClientInformation, CookieRequest, CookieResponse, CustomPayload, Disconnect, KeepAlive,
-            Ping, ResourcePackPop, ResourcePackPush, ResourcePackResponse, StoreCookie, Transfer,
-            UpdateTags,
+            ClientInformation, CookieRequest, CookieResponse, CustomClickAction, CustomPayload,
+            Disconnect, KeepAlive, Ping, ResourcePackPop, ResourcePackPush, ResourcePackResponse,
+            StoreCookie, Transfer, UpdateTags,
         },
         login::Property,
     },
@@ -190,6 +190,35 @@ impl Codec<i32> for HolderId {
         w.varint(v + 1)
     }
 }
+/// `Holder<Dialog>` as Dialog.STREAM_CODEC sends it: an entry of the
+/// `minecraft:dialog` registry the server sent in configuration, or the
+/// dialog itself.
+#[derive(Clone, Debug, PartialEq)]
+pub enum DialogHolder {
+    Registry(i32),
+    Direct(Tag),
+}
+impl Codec<DialogHolder> for DialogHolder {
+    fn read(r: &mut Reader) -> Result<Self> {
+        Ok(match r.varint()? {
+            0 => Self::Direct(r.nbt()?),
+            id => Self::Registry(id - 1),
+        })
+    }
+    fn write(v: &Self, w: &mut Writer) {
+        match v {
+            Self::Registry(id) => w.varint(id + 1),
+            Self::Direct(tag) => {
+                w.varint(0);
+                w.nbt(tag);
+            }
+        }
+    }
+}
+packet!(
+    /// ClientboundShowDialogPacket.
+    ShowDialog { dialog: DialogHolder => DialogHolder }
+);
 packet!(
     /// ChatType.Bound.
     ChatTypeBound { chat_type: i32 => HolderId, name: Tag => Nbt, target: Option<Tag> => Opt<Nbt> }
@@ -1854,6 +1883,8 @@ packet_enum!(Clientbound, crate::ids::play::clientbound {
     UpdateMobEffect(UpdateMobEffect) = UPDATE_MOB_EFFECT,
     UpdateTags(UpdateTags) = UPDATE_TAGS,
     TrackedWaypoint(TrackedWaypoint) = WAYPOINT,
+    ClearDialog(Empty) = CLEAR_DIALOG,
+    ShowDialog(ShowDialog) = SHOW_DIALOG,
 });
 packet!(
     /// ClientboundClearTitlesPacket: whether to also reset the timings.
@@ -2229,6 +2260,7 @@ packet_enum!(Serverbound, crate::ids::play::serverbound {
     ContainerClose(ContainerClose) = CONTAINER_CLOSE,
     CookieResponse(CookieResponse) = COOKIE_RESPONSE,
     CustomPayload(CustomPayload) = CUSTOM_PAYLOAD,
+    CustomClickAction(CustomClickAction) = CUSTOM_CLICK_ACTION,
     EditBook(EditBook) = EDIT_BOOK,
     Interact(Interact) = INTERACT,
     KeepAlive(KeepAlive) = KEEP_ALIVE,
@@ -3024,6 +3056,7 @@ mod tests {
         w.varint(101);
         assert!(BookPages::read(&mut Reader::new(&w.data)).is_err());
     }
+
     #[test]
     fn boss_event_round_trips() {
         let add = Clientbound::BossEvent(BossEvent {
@@ -3061,4 +3094,28 @@ mod tests {
             Clientbound::decode,
         );
     }
+
+    /// A registry entry is its id + 1, the dialog itself a 0 then its NBT.
+    #[test]
+    fn dialogs_round_trip() {
+        let notice = Tag::compound([("type", Tag::String("minecraft:notice".into()))]);
+        for dialog in [DialogHolder::Registry(3), DialogHolder::Direct(notice)] {
+            crate::packets::round_trip(
+                Clientbound::ShowDialog(ShowDialog { dialog }),
+                Clientbound::encode,
+                Clientbound::decode,
+            );
+        }
+        let mut w = Writer::new();
+        DialogHolder::write(&DialogHolder::Registry(3), &mut w);
+        assert_eq!(w.data, [4]);
+        crate::packets::round_trip(
+            Serverbound::CustomClickAction(CustomClickAction {
+                id: "minecraft:custom".into(),
+                payload: None,
+            }),
+            Serverbound::encode,
+            Serverbound::decode,
+        );
+    }
 }
diff --git a/tools/server_e2e.py b/tools/server_e2e.py
new file mode 100644
index 000000000..397e03549
--- /dev/null
+++ b/tools/server_e2e.py
@@ -0,0 +1,194 @@
+#!/usr/bin/env python3
+"""Horizon's client on a vanilla 26.3 dedicated server, end to end.
+
+A vanilla server (the pinned server jar, offline mode, a flat world) and one Horizon game joined to it,
+driven by horizon-ctl. The server's console does what a server or its plugins do; the checks read what
+the game shows and what reaches the server (its console and, for custom click actions, its debug log).
+
+    python3 tools/server_e2e.py --bin-dir target/fast             # every check
+    python3 tools/server_e2e.py --bin-dir target/fast --check dialog
+
+Checks:
+- dialog: `/dialog show` with a multi-action dialog (a message, three buttons): the game shows it,
+          a command runs on the server (`trigger`), a custom action reaches it with its
+          payload (the server's "Received custom click action" line), `wait_for_response` leaves the
+          waiting screen, and `/dialog clear` closes a dialog (servers used to see nothing: the game
+          dropped the packets).
+
+The game runs with fresh HORIZON_HOME, launcher and XDG folders and without audio. Screenshots and both
+logs go to --out.
+"""
+import argparse
+import json
+import os
+import shutil
+import subprocess
+import sys
+import tempfile
+import time
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).resolve().parent))
+import lab  # noqa: E402
+import test_rust_parity as base  # noqa: E402
+from agent_control_e2e import Failed  # noqa: E402
+from lan_e2e import Game  # noqa: E402
+from test_dedicated_server_parity import Server  # noqa: E402
+
+ROOT = Path(__file__).resolve().parents[1]
+PLAYER = 'Steve'
+PROPERTIES = {
+    'online-mode': 'false',
+    'white-list': 'false',
+    'level-type': 'minecraft\\:flat',
+    'generate-structures': 'false',
+    'spawn-protection': '0',
+    'view-distance': '3',
+    'simulation-distance': '3',
+    'pause-when-empty-seconds': '-1',
+}
+# MinecraftServer.handleCustomClickAction logs at debug level: the console shows that logger's debug lines.
+LOG4J = """<?xml version="1.0" encoding="UTF-8"?>
+<Configuration status="WARN">
+  <Appenders><Console name="out" target="SYSTEM_OUT"><PatternLayout pattern="[%level] %msg%n"/></Console></Appenders>
+  <Loggers>
+    <Logger name="net.minecraft.server.MinecraftServer" level="debug"/>
+    <Root level="info"><AppenderRef ref="out"/></Root>
+  </Loggers>
+</Configuration>
+"""
+
+
+def snbt(value):
+    """A JSON value as SNBT (strings quoted, booleans as bytes)."""
+    if isinstance(value, bool):
+        return '1b' if value else '0b'
+    if isinstance(value, str):
+        return json.dumps(value)
+    if isinstance(value, list):
+        return '[' + ','.join(snbt(v) for v in value) + ']'
+    if isinstance(value, dict):
+        return '{' + ','.join(f'{k}:{snbt(v)}' for k, v in value.items()) + '}'
+    return str(value)
+
+
+def check_dialog(server, game, out):
+    server.console('scoreboard objectives add answer trigger')
+    server.console(f'scoreboard players enable {PLAYER} answer')
+    dialog = {
+        'type': 'minecraft:multi_action',
+        'title': {'text': 'Sign in', 'color': 'gold'},
+        'body': {'type': 'minecraft:plain_message', 'contents': 'Pick a number.'},
+        'actions': [
+            {'label': 'Send', 'action': {'type': 'minecraft:run_command', 'command': 'trigger answer set 41'}},
+            {'label': 'Submit', 'action': {'type': 'minecraft:dynamic/custom', 'id': 'horizon:e2e',
+                                           'additions': {'tag': 'x'}}},
+            {'label': 'Wait', 'action': {'type': 'minecraft:dynamic/custom', 'id': 'horizon:wait'}},
+        ],
+        'after_action': 'none',
+        'pause': False,  # a pausing dialog must close after an action
+    }
+    shown = {}
+    server.console(f'dialog show {PLAYER} {snbt(dialog)}')
+    game.raw('wait-for', 'screen', 'dialog', '--timeout', 30)
+    state = game('state')
+    shown['shown'] = state['dialog']['open']
+    assert shown['shown']['title'] == 'Sign in', shown
+    assert shown['shown']['buttons'] == ['Send', 'Submit', 'Wait'], shown
+    game.shot(out, 'dialog')
+    game.raw('click', 'send')
+    time.sleep(1)
+    server.console(f'scoreboard players get {PLAYER} answer')
+    server.wait_for(rf'{PLAYER} has 41 \[answer\]', timeout=30)
+    shown['trigger'] = 41
+    # A custom action and its additions.
+    game.raw('click', 'submit')
+    server.wait_for(r'Received custom click action horizon:e2e with payload', timeout=30)
+    line = next(l for l in server.lines if 'horizon:e2e' in l)
+    shown['custom'] = line.split('payload ', 1)[1]
+    assert shown['custom'] == '{tag:"x"}', shown
+    # after_action none: still open. Then clear it.
+    assert game('state')['dialog']['open'], 'the dialog closed after an action with after_action none'
+    server.console(f'dialog clear {PLAYER}')
+    game.raw('wait-for', 'screen', 'playing', '--timeout', 30)
+    # wait_for_response: the waiting screen until the server answers (here, never).
+    server.console(f'dialog show {PLAYER} {snbt(dict(dialog, after_action="wait_for_response"))}')
+    game.raw('wait-for', 'screen', 'dialog', '--timeout', 30)
+    game.raw('click', 'wait')
+    server.wait_for(r'Received custom click action horizon:wait', timeout=30)
+    shown['waiting'] = game('state')['dialog']['screen']
+    game.shot(out, 'waiting')
+    assert shown['waiting'] == 'waiting_for_response', shown
+    # Its Back works after 5 s, and so does Escape (clear_dialog leaves it open, as in vanilla).
+    time.sleep(5.5)
+    game.raw('key', 'esc', 'tap')
+    game.raw('wait-for', 'screen', 'playing', '--timeout', 10)
+    return shown
+
+
+CHECKS = {'dialog': check_dialog}
+
+
+def run(bins, out, checks):
+    lock, jars, libraries = base.verify_artifacts()
+    work = Path(tempfile.mkdtemp(prefix='hz-server-e2e-'))
+    port = lab.free_port()
+    directory = work / 'server'
+    directory.mkdir()
+    props = dict(PROPERTIES, **{'server-port': str(port)})
+    (directory / 'server.properties').write_text(''.join(f'{k}={v}\n' for k, v in props.items()))
+    (directory / 'eula.txt').write_text('eula=true\n')
+    (work / 'log4j2.xml').write_text(LOG4J)
+    classpath = os.pathsep.join(map(str, [jars['server'], *libraries]))
+    server = Server(['java', '-Xmx2g', f'-Dlog4j.configurationFile={work / "log4j2.xml"}', '-cp', classpath,
+                     'net.minecraft.server.Main', 'nogui'], directory, 'vanilla')
+    game = Game('client', bins / 'horizon-ctl', lab.RESOURCES.resolve())
+    for key in ('XDG_DATA_HOME', 'XDG_CONFIG_HOME', 'HORIZON_LAUNCHER_HOME'):
+        game.d.env[key] = str(game.work / key.lower())
+    game.d.env['HORIZON_LAUNCHER_NO_SELF_UPDATE'] = '1'
+    results = {}
+    try:
+        server.wait_for(r'Done \(')
+        server.console('gamerule spawn_mobs false')
+        game('launch', wait=False, offscreen=sys.platform == 'darwin')
+        game.raw('connect', f'127.0.0.1:{port}', PLAYER)
+        game.raw('wait-for', 'loaded', '--timeout', 300)
+        server.wait_for(rf'{PLAYER} joined the game')
+        server.console(f'op {PLAYER}')
+        game.wait(20)
+        for name in checks:
+            try:
+                results[name] = {'pass': True, 'detail': CHECKS[name](server, game, out)}
+            except (Failed, AssertionError, StopIteration, KeyError) as e:
+                results[name] = {'pass': False, 'detail': repr(e)}
+            print(f'[server] {name}: {"PASS" if results[name]["pass"] else "FAIL"} {results[name]["detail"]}')
+    finally:
+        (out / 'client.log').write_text(game.close())
+        server.stop()
+        shutil.copy(server.log_path, out / 'server.log')
+        shutil.rmtree(game.work, ignore_errors=True)
+        shutil.rmtree(work, ignore_errors=True)
+    return results
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__, formatter_class=argparse.RawDescriptionHelpFormatter)
+    parser.add_argument('--bin-dir', help='prebuilt horizon-client and horizon-ctl (default: build with the fast profile)')
+    parser.add_argument('--check', action='append', choices=list(CHECKS), help='run only these checks (repeatable)')
+    parser.add_argument('--out', default=str(ROOT / '.local/server-e2e'), help='screenshots and logs go here')
+    args = parser.parse_args()
+    if args.bin_dir:
+        bins = Path(args.bin_dir).resolve()
+    else:
+        subprocess.run(['cargo', 'build', '--locked', '--profile', 'fast', '-p', 'horizon-client', '--bins'],
+                       cwd=ROOT, check=True)
+        bins = ROOT / 'target/fast'
+    out = Path(args.out)
+    out.mkdir(parents=True, exist_ok=True)
+    results = run(bins, out, args.check or list(CHECKS))
+    print(json.dumps(results, indent=1))
+    sys.exit(0 if results and all(r['pass'] for r in results.values()) else 1)
+
+
+if __name__ == '__main__':
+    main()