diff --git a/crates/ui-egui/src/chrome.rs b/crates/ui-egui/src/chrome.rs
index dfb5e69..23876f3 100644
--- a/crates/ui-egui/src/chrome.rs
+++ b/crates/ui-egui/src/chrome.rs
@@ -21,86 +21,105 @@ pub fn app_bar(app: &mut DesignApp, ui: &mut egui::Ui) {
             let full = ui.max_rect();
             let mut menus_end = full.min.x;
             let mut tools_start = full.max.x;
-            ui.horizontal_centered(|ui| {
-                if icons::button(ui, "home", 24.0, app.session.active().is_none(), crate::i18n::tr(&app.ui.language, "Home")).clicked() {
-                    app.session_home();
-                }
-                ui.add_space(6.0);
-                if !app.native_menu {
-                    ui.style_mut().visuals.widgets.inactive.weak_bg_fill = Color32::TRANSPARENT;
-                    ui.style_mut().visuals.widgets.inactive.bg_stroke = Stroke::NONE;
-                    ui.style_mut().visuals.widgets.hovered.bg_stroke = Stroke::NONE;
-                    ui.style_mut().spacing.button_padding = vec2(7.0, 3.0);
-                    crate::menus::menu_bar(app, ui);
-                }
-                menus_end = ui.min_rect().max.x;
-                ui.with_layout(egui::Layout::right_to_left(egui::Align::Center), |ui| {
-                    ui.add_space(4.0);
-                    // Search field.
-                    let (r, _) = ui.allocate_exact_size(vec2(125.0, 18.0), Sense::click());
-                    ui.painter().rect(r, 1.0, t.input, Stroke::new(1.0, t.field_border), egui::StrokeKind::Inside);
-                    icons::paint(ui.painter(), egui::Rect::from_min_size(r.min + vec2(3.0, 2.0), vec2(14.0, 14.0)), "search", t.icon);
-                    crate::rtl::paint(
-                        ui.painter(),
-                        r.min + vec2(20.0, 9.0),
-                        egui::Align2::LEFT_CENTER,
-                        crate::i18n::tr(&app.ui.language, "Search"),
-                        egui::FontId::proportional(11.0),
-                        t.text_dim,
-                    );
-                    ui.add_space(8.0);
-                    let current = app.ui.workspace.clone();
-                    let shown = crate::i18n::workspace_name(&app.ui.language, &current);
-                    ui.menu_button(crate::rtl::widget(ui, egui::RichText::new(format!("{shown} ▾")).font(semibold(11.5)).color(t.text)), |ui| {
-                        let customs: Vec<String> = app.ui.custom_workspaces.iter().map(|w| w.name.clone()).collect();
-                        for w in
-                            ["Essentials", "Advanced", "Book", "Digital Publishing", "Interactive for PDF", "Printing and Proofing", "Typography"]
-                                .into_iter()
-                                .map(str::to_string)
-                                .chain(customs.iter().cloned())
-                        {
-                            if ui.selectable_label(w == current, crate::rtl::widget(ui, crate::i18n::workspace_name(&app.ui.language, &w))).clicked()
+            // The right-hand controls' width, measured last frame: in a window too narrow for them
+            // and the menus they follow the menus, and the bar scrolls sideways.
+            let tools_w_id = ui.id().with("tools_width");
+            let tools_w: f32 = ui.data(|d| d.get_temp(tools_w_id)).unwrap_or(0.0);
+            crate::widgets::overflow_scrolling(ui);
+            egui::ScrollArea::horizontal().id_salt("app_bar_scroll").auto_shrink([false, false]).show(ui, |ui| {
+                ui.horizontal_centered(|ui| {
+                    if icons::button(ui, "home", 24.0, app.session.active().is_none(), crate::i18n::tr(&app.ui.language, "Home")).clicked() {
+                        app.session_home();
+                    }
+                    ui.add_space(6.0);
+                    if !app.native_menu {
+                        ui.style_mut().visuals.widgets.inactive.weak_bg_fill = Color32::TRANSPARENT;
+                        ui.style_mut().visuals.widgets.inactive.bg_stroke = Stroke::NONE;
+                        ui.style_mut().visuals.widgets.hovered.bg_stroke = Stroke::NONE;
+                        ui.style_mut().spacing.button_padding = vec2(7.0, 3.0);
+                        crate::menus::menu_bar(app, ui);
+                    }
+                    menus_end = ui.min_rect().max.x;
+                    let size = vec2(ui.available_width().max(tools_w), ui.available_height());
+                    let tools = ui.allocate_ui_with_layout(size, egui::Layout::right_to_left(egui::Align::Center), |ui| {
+                        ui.add_space(4.0);
+                        // Search field.
+                        let (r, _) = ui.allocate_exact_size(vec2(125.0, 18.0), Sense::click());
+                        ui.painter().rect(r, 1.0, t.input, Stroke::new(1.0, t.field_border), egui::StrokeKind::Inside);
+                        icons::paint(ui.painter(), egui::Rect::from_min_size(r.min + vec2(3.0, 2.0), vec2(14.0, 14.0)), "search", t.icon);
+                        crate::rtl::paint(
+                            ui.painter(),
+                            r.min + vec2(20.0, 9.0),
+                            egui::Align2::LEFT_CENTER,
+                            crate::i18n::tr(&app.ui.language, "Search"),
+                            egui::FontId::proportional(11.0),
+                            t.text_dim,
+                        );
+                        ui.add_space(8.0);
+                        let current = app.ui.workspace.clone();
+                        let shown = crate::i18n::workspace_name(&app.ui.language, &current);
+                        ui.menu_button(crate::rtl::widget(ui, egui::RichText::new(format!("{shown} ▾")).font(semibold(11.5)).color(t.text)), |ui| {
+                            let customs: Vec<String> = app.ui.custom_workspaces.iter().map(|w| w.name.clone()).collect();
+                            for w in
+                                ["Essentials", "Advanced", "Book", "Digital Publishing", "Interactive for PDF", "Printing and Proofing", "Typography"]
+                                    .into_iter()
+                                    .map(str::to_string)
+                                    .chain(customs.iter().cloned())
                             {
-                                let _ = app.run("window.workspace", json!({"name": w}));
+                                if ui
+                                    .selectable_label(w == current, crate::rtl::widget(ui, crate::i18n::workspace_name(&app.ui.language, &w)))
+                                    .clicked()
+                                {
+                                    let _ = app.run("window.workspace", json!({"name": w}));
+                                    ui.close();
+                                }
+                            }
+                            ui.separator();
+                            if ui
+                                .button(crate::rtl::widget(
+                                    ui,
+                                    format!(
+                                        "{} {}",
+                                        crate::i18n::tr(&app.ui.language, "Reset"),
+                                        crate::i18n::workspace_name(&app.ui.language, &current)
+                                    ),
+                                ))
+                                .clicked()
+                            {
+                                let _ = app.run("window.resetWorkspace", json!({}));
                                 ui.close();
                             }
-                        }
-                        ui.separator();
-                        if ui
-                            .button(crate::rtl::widget(
-                                ui,
-                                format!("{} {}", crate::i18n::tr(&app.ui.language, "Reset"), crate::i18n::workspace_name(&app.ui.language, &current)),
-                            ))
-                            .clicked()
-                        {
-                            let _ = app.run("window.resetWorkspace", json!({}));
-                            ui.close();
-                        }
-                        if ui.button(crate::rtl::widget(ui, crate::i18n::tr(&app.ui.language, "New Workspace…"))).clicked() {
-                            let _ = app.run("window.newWorkspace", json!({}));
-                            ui.close();
-                        }
-                        if !customs.is_empty() {
-                            ui.menu_button(crate::rtl::widget(ui, crate::i18n::tr(&app.ui.language, "Delete Workspace")), |ui| {
-                                for w in &customs {
-                                    if ui.button(w).clicked() {
-                                        let _ = app.run("window.deleteWorkspace", json!({"name": w}));
-                                        ui.close();
+                            if ui.button(crate::rtl::widget(ui, crate::i18n::tr(&app.ui.language, "New Workspace…"))).clicked() {
+                                let _ = app.run("window.newWorkspace", json!({}));
+                                ui.close();
+                            }
+                            if !customs.is_empty() {
+                                ui.menu_button(crate::rtl::widget(ui, crate::i18n::tr(&app.ui.language, "Delete Workspace")), |ui| {
+                                    for w in &customs {
+                                        if ui.button(w).clicked() {
+                                            let _ = app.run("window.deleteWorkspace", json!({"name": w}));
+                                            ui.close();
+                                        }
                                     }
-                                }
-                            });
+                                });
+                            }
+                        });
+                        ui.add_space(6.0);
+                        if icons::button(ui, "share", 22.0, false, crate::i18n::tr(&app.ui.language, "Share")).clicked() {
+                            app.status("Export a PDF, IDML or package to share — no cloud account needed.");
                         }
+                        ui.add_space(8.0);
+                        // Always one click away: the ArtCraft community Discord.
+                        if crate::about::discord_button(ui, "Discord", vec2(78.0, 22.0)) {
+                            let _ = app.run("help.discord", json!({}));
+                        }
+                        tools_start = ui.min_rect().min.x;
+                        ui.min_rect().width()
                     });
-                    ui.add_space(6.0);
-                    if icons::button(ui, "share", 22.0, false, crate::i18n::tr(&app.ui.language, "Share")).clicked() {
-                        app.status("Export a PDF, IDML or package to share — no cloud account needed.");
+                    if (tools.inner - tools_w).abs() > 0.5 {
+                        ui.data_mut(|d| d.insert_temp(tools_w_id, tools.inner));
+                        ui.ctx().request_discard("app bar: the right-hand controls changed width");
                     }
-                    ui.add_space(8.0);
-                    // Always one click away: the ArtCraft community Discord.
-                    if crate::about::discord_button(ui, "Discord", vec2(78.0, 22.0)) {
-                        let _ = app.run("help.discord", json!({}));
-                    }
-                    tools_start = ui.min_rect().min.x;
                 });
             });
             // Centred title.
@@ -142,14 +161,18 @@ pub fn control_bar(app: &mut DesignApp, ui: &mut egui::Ui) {
             egui::Frame::NONE.fill(t.panel).inner_margin(egui::Margin { left: 8, right: 8, top: 5, bottom: 3 }).stroke(Stroke::new(1.0, t.divider)),
         )
         .show(ui, |ui| {
-            ui.horizontal(|ui| {
-                let text_mode =
-                    matches!(app.session.tool_id(), "type" | "verticalType") || app.session.active().is_some_and(|d| d.selection.text.is_some());
-                if text_mode {
-                    control_text(app, ui);
-                } else {
-                    control_object(app, ui);
-                }
+            // Wider than the window: the bar scrolls sideways.
+            crate::widgets::overflow_scrolling(ui);
+            egui::ScrollArea::horizontal().id_salt("control_bar_scroll").auto_shrink([false, true]).show(ui, |ui| {
+                ui.horizontal(|ui| {
+                    let text_mode =
+                        matches!(app.session.tool_id(), "type" | "verticalType") || app.session.active().is_some_and(|d| d.selection.text.is_some());
+                    if text_mode {
+                        control_text(app, ui);
+                    } else {
+                        control_object(app, ui);
+                    }
+                });
             });
         });
 }
@@ -716,3 +739,86 @@ fn community_card(app: &mut DesignApp, ui: &mut egui::Ui) {
         });
     });
 }
+
+#[cfg(test)]
+mod tests {
+    use egui::{pos2, vec2};
+    use egui_kittest::kittest::Queryable;
+
+    use crate::test_window::{self, wheel};
+
+    /// The Control panel's last control with nothing selected.
+    const LAST_CONTROL: &str = "Jump to Next Column";
+    const FIRST_CONTROL: &str = "Rotate 90° Counterclockwise";
+
+    fn app() -> crate::DesignApp {
+        let mut app = crate::DesignApp::new(designcraft_engine::Session::new(), crate::Services::default());
+        app.ui.control_bar = true;
+        app
+    }
+
+    fn rect(h: &egui_kittest::Harness<'static, test_window::Window>, label: &str) -> egui::Rect {
+        h.get_by_label(label).rect()
+    }
+
+    #[test]
+    fn a_narrow_window_scrolls_the_control_bar() {
+        let w = 700.0;
+        let mut h = test_window::open(app(), vec2(w, 600.0));
+        let bar = test_window::panel_rect(&h, "control_bar");
+        assert!(rect(&h, LAST_CONTROL).max.x > w, "the controls are wider than the window");
+        // A plain mouse wheel scrolls the bar sideways.
+        let first = rect(&h, FIRST_CONTROL).center();
+        wheel(&mut h, first, vec2(0.0, -3000.0));
+        let last = rect(&h, LAST_CONTROL);
+        let window = egui::Rect::from_min_size(pos2(0.0, 0.0), vec2(w, 600.0));
+        assert!(window.contains_rect(last) && bar.contains_rect(last), "{last:?} outside the bar {bar:?}");
+        assert_eq!(test_window::panel_rect(&h, "control_bar").height(), bar.height(), "the bar keeps its height");
+        // A popup opened from a scrolled control opens at that control.
+        let fill = h.get_by_label("Fill").rect();
+        let chip = pos2(fill.max.x + 15.0, fill.center().y);
+        h.hover_at(chip);
+        h.drag_at(chip);
+        h.drop_at(chip);
+        h.run_steps(4);
+        let item = rect(&h, "[Black]");
+        assert!(item.min.y > fill.max.y && (item.min.x - chip.x).abs() < 120.0, "popup item at {item:?}, control at {chip:?}");
+    }
+
+    #[test]
+    fn a_narrow_window_scrolls_the_app_bar() {
+        let w = 640.0;
+        let mut h = test_window::open(app(), vec2(w, 600.0));
+        let (help, share) = (rect(&h, "Help"), rect(&h, "Share"));
+        assert!(help.max.x <= share.min.x, "the menus ({help:?}) and the workspace controls ({share:?}) overlap");
+        wheel(&mut h, help.center(), vec2(0.0, -3000.0));
+        let share = rect(&h, "Share");
+        let window = egui::Rect::from_min_size(pos2(0.0, 0.0), vec2(w, 600.0));
+        assert!(window.contains_rect(share), "{share:?} outside the window");
+    }
+
+    #[test]
+    fn a_wide_window_does_not_scroll_the_bars() {
+        let mut h = test_window::open(app(), vec2(1400.0, 900.0));
+        let before = [rect(&h, FIRST_CONTROL), rect(&h, LAST_CONTROL), rect(&h, "Help"), rect(&h, "Share")];
+        assert!(before.iter().all(|r| r.max.x <= 1400.0), "{before:?}");
+        wheel(&mut h, before[0].center(), vec2(0.0, -3000.0));
+        wheel(&mut h, before[2].center(), vec2(0.0, -3000.0));
+        let after = [rect(&h, FIRST_CONTROL), rect(&h, LAST_CONTROL), rect(&h, "Help"), rect(&h, "Share")];
+        assert_eq!(after, before);
+    }
+
+    #[test]
+    fn a_scrolled_bar_keeps_its_captions_on_one_line() {
+        let mut app = app();
+        app.run("file.new", serde_json::json!({})).unwrap();
+        let f = app.run("frame.create", serde_json::json!({"rect": [72, 72, 300, 200], "content": "text", "text": "Hello"})).unwrap();
+        app.run("selection.set", serde_json::json!({"ids": [f["id"]]})).unwrap();
+        let mut h = test_window::open(app, vec2(700.0, 600.0));
+        let bar = test_window::panel_rect(&h, "control_bar").center();
+        wheel(&mut h, bar, vec2(0.0, -3000.0));
+        // The text frame's last group: its caption gets only what is left of the row.
+        let columns = h.get_by_label("Columns").rect();
+        assert!(columns.height() < 20.0 && columns.width() > columns.height(), "Columns wraps: {columns:?}");
+    }
+}
diff --git a/crates/ui-egui/src/icons.rs b/crates/ui-egui/src/icons.rs
index 7e21460..69415e9 100644
--- a/crates/ui-egui/src/icons.rs
+++ b/crates/ui-egui/src/icons.rs
@@ -805,6 +805,8 @@ pub fn button(ui: &mut egui::Ui, name: &str, size: f32, selected: bool, tip: &st
     }
     let pad = size * 0.16;
     paint(ui.painter(), r.shrink(pad), name, if selected { t.text_strong } else { t.icon });
+    let enabled = ui.is_enabled();
+    resp.widget_info(|| egui::WidgetInfo::selected(egui::WidgetType::Button, enabled, selected, tip));
     if tip.is_empty() {
         resp
     } else {
diff --git a/crates/ui-egui/src/lib.rs b/crates/ui-egui/src/lib.rs
index 43a0816..275018c 100644
--- a/crates/ui-egui/src/lib.rs
+++ b/crates/ui-egui/src/lib.rs
@@ -984,3 +984,54 @@ mod tests {
         assert!(app.ui.dialog.is_none(), "a control-channel app.open doesn't raise an alert");
     }
 }
+
+/// The whole window in a headless test harness, at a chosen window size.
+#[cfg(test)]
+pub(crate) mod test_window {
+    use egui_kittest::Harness;
+
+    pub struct Window {
+        pub app: crate::DesignApp,
+        ready: bool,
+    }
+
+    /// The window at `size` with a new document open.
+    pub fn open(mut app: crate::DesignApp, size: egui::Vec2) -> Harness<'static, Window> {
+        if app.session.active().is_none() {
+            app.run("file.new", serde_json::json!({})).unwrap();
+        }
+        let mut h = Harness::builder().with_size(size).with_max_steps(1000).build_ui_state(
+            |ui, w: &mut Window| {
+                // The builder runs a frame before the texture size can be raised: skip it.
+                if !w.ready {
+                    return;
+                }
+                let ctx = ui.ctx().clone();
+                w.app.logic(&ctx);
+                w.app.ui(ui);
+            },
+            Window { app, ready: false },
+        );
+        h.input_mut().max_texture_side = Some(8192);
+        h.state_mut().ready = true;
+        h.run_steps(6);
+        h
+    }
+
+    /// The mouse wheel turned over `pos`: positive `delta` moves the content right and down.
+    pub fn wheel(h: &mut Harness<'static, Window>, pos: egui::Pos2, delta: egui::Vec2) {
+        h.hover_at(pos);
+        h.event(egui::Event::MouseWheel {
+            unit: egui::MouseWheelUnit::Point,
+            delta,
+            phase: egui::TouchPhase::Move,
+            modifiers: egui::Modifiers::NONE,
+        });
+        h.run_steps(10);
+    }
+
+    /// The outer rect of a side or top panel, from egui's memory.
+    pub fn panel_rect(h: &Harness<'static, Window>, id: &str) -> egui::Rect {
+        egui::containers::panel::PanelState::load(&h.ctx, egui::Id::new(id)).map(|s| s.outer_rect).unwrap()
+    }
+}
diff --git a/crates/ui-egui/src/toolbar.rs b/crates/ui-egui/src/toolbar.rs
index a3d4954..5a5e1f0 100644
--- a/crates/ui-egui/src/toolbar.rs
+++ b/crates/ui-egui/src/toolbar.rs
@@ -12,27 +12,33 @@ const BTN: f32 = 24.0;
 
 pub fn show(app: &mut DesignApp, ui: &mut egui::Ui) {
     let t = Tokens::get(ui.ctx());
-    let cols = if app.ui.tools_double_column { 2 } else { 1 };
+    let frame = egui::Frame::NONE.fill(t.panel).stroke(Stroke::new(1.0, t.divider));
+    // A single column that doesn't fit the window's height becomes two, without changing the
+    // preference; whatever two columns still can't fit scrolls.
+    let single_h_id = egui::Id::new("tools_single_column_height");
+    let single_h: Option<f32> = ui.data(|d| d.get_temp(single_h_id));
+    let viewport_h = ui.available_height() - frame.total_margin().sum().y;
+    let crowded = !app.ui.tools_double_column && single_h.is_some_and(|h| h > viewport_h);
+    let cols = if app.ui.tools_double_column || crowded { 2 } else { 1 };
     let width = 8.0 + BTN * cols as f32 + 4.0 * (cols as f32 - 1.0) + 8.0;
-    let r = egui::Panel::left("tools")
-        .exact_size(width)
-        .resizable(false)
-        .frame(egui::Frame::NONE.fill(t.panel).stroke(Stroke::new(1.0, t.divider)))
-        .show(ui, |ui| {
+    let r = egui::Panel::left("tools").exact_size(width).resizable(false).frame(frame).show(ui, |ui| {
+        crate::widgets::overflow_scrolling(ui);
+        let scroll = egui::ScrollArea::vertical().id_salt("tools_scroll").auto_shrink([false, false]).show(ui, |ui| {
             ui.spacing_mut().item_spacing.y = 1.0;
             ui.add_space(3.0);
-            // Collapse chevrons.
+            // Collapse chevrons (nothing to toggle while the window forces two columns).
             ui.horizontal(|ui| {
                 ui.add_space(width / 2.0 - 8.0);
-                if icons::button(
-                    ui,
-                    if cols == 1 { "double-chevron-right" } else { "double-chevron-left" },
-                    16.0,
-                    false,
-                    crate::i18n::tr(&app.ui.language, "Toggle double column"),
-                )
-                .clicked()
-                {
+                let toggle = ui.add_enabled_ui(!crowded, |ui| {
+                    icons::button(
+                        ui,
+                        if cols == 1 { "double-chevron-right" } else { "double-chevron-left" },
+                        16.0,
+                        false,
+                        crate::i18n::tr(&app.ui.language, "Toggle double column"),
+                    )
+                });
+                if toggle.inner.clicked() {
                     app.ui.tools_double_column = !app.ui.tools_double_column;
                 }
             });
@@ -169,6 +175,15 @@ pub fn show(app: &mut DesignApp, ui: &mut egui::Ui) {
             ui.add_space(8.0);
             fill_stroke_proxy(app, ui, width);
         });
+        if cols == 1 {
+            let h = scroll.content_size.y;
+            ui.data_mut(|d| d.insert_temp(single_h_id, h));
+            // Laid out in one column that turned out too tall: lay out again in two.
+            if h > viewport_h {
+                ui.ctx().request_discard("tools panel: one column does not fit");
+            }
+        }
+    });
     if std::env::var_os("DESIGNCRAFT_DEBUG_LAYOUT").is_some() {
         eprintln!("tools panel rect {:?} (wanted width {width}); remaining {:?}", r.response.rect, ui.available_rect_before_wrap());
     }
@@ -252,9 +267,11 @@ fn fill_stroke_proxy(app: &mut DesignApp, ui: &mut egui::Ui, width: f32) {
         paint_stroke(p);
         paint_fill(p);
     }
+    let fill_tip = crate::i18n::tr(&app.ui.language, "Fill (X)");
     let fresp = ui.interact(fill_r, ui.id().with("proxy_fill"), Sense::click()).on_hover_ui(|ui| {
-        crate::rtl::label(ui, crate::i18n::tr(&app.ui.language, "Fill (X)"));
+        crate::rtl::label(ui, fill_tip);
     });
+    fresp.widget_info(|| egui::WidgetInfo::labeled(egui::WidgetType::Button, true, fill_tip));
     let sresp = ui.interact(stroke_r.translate(vec2(0.0, 0.0)), ui.id().with("proxy_stroke"), Sense::click()).on_hover_ui(|ui| {
         crate::rtl::label(ui, crate::i18n::tr(&app.ui.language, "Stroke (X)"));
     });
@@ -387,7 +404,82 @@ fn tool_button(ui: &mut egui::Ui, icon: &str, active: bool, tip: &str) -> egui::
         ui.painter().rect_filled(egui::Rect::from_center_size(r.center(), egui::vec2(28.0, 20.0)), 2.0, t.hover);
     }
     icons::paint(ui.painter(), egui::Rect::from_center_size(r.center(), egui::vec2(17.0, 17.0)), icon, if active { t.text_strong } else { t.icon });
+    let enabled = ui.is_enabled();
+    resp.widget_info(|| egui::WidgetInfo::labeled(egui::WidgetType::Button, enabled, tip));
     resp.on_hover_ui(|ui| {
         crate::rtl::label(ui, tip);
     })
 }
+
+#[cfg(test)]
+mod tests {
+    use egui::{pos2, vec2};
+    use egui_kittest::kittest::Queryable;
+
+    use crate::test_window::{self, wheel};
+
+    /// The last tool group's button and the Fill proxy, near the bottom of the panel.
+    const LAST_TOOL: &str = "Zoom Tool (Z)";
+    const FILL: &str = "Fill (X)";
+    /// Status bar height: the Tools panel ends above it.
+    const STATUS_H: f32 = 17.0;
+
+    fn app(double: bool) -> crate::DesignApp {
+        let mut app = crate::DesignApp::new(designcraft_engine::Session::new(), crate::Services::default());
+        app.ui.tools_double_column = double;
+        app
+    }
+
+    fn column_width(cols: f32) -> f32 {
+        8.0 + super::BTN * cols + 4.0 * (cols - 1.0) + 8.0
+    }
+
+    fn rect(h: &egui_kittest::Harness<'static, test_window::Window>, label: &str) -> egui::Rect {
+        h.get_by_label(label).rect()
+    }
+
+    #[test]
+    fn a_short_window_reaches_every_tool() {
+        for double in [false, true] {
+            let (w, ht) = (1000.0, 500.0);
+            let mut h = test_window::open(app(double), vec2(w, ht));
+            let panel = test_window::panel_rect(&h, "tools");
+            wheel(&mut h, panel.center(), vec2(0.0, -2000.0));
+            let visible = egui::Rect::from_min_max(pos2(0.0, panel.min.y), pos2(w, ht - STATUS_H));
+            for label in [LAST_TOOL, FILL] {
+                let r = rect(&h, label);
+                assert!(visible.contains_rect(r), "double column {double}: {label} at {r:?} is outside {visible:?}");
+            }
+            assert_eq!(h.state().app.ui.tools_double_column, double, "the preference is the user's");
+        }
+    }
+
+    #[test]
+    fn tools_take_two_columns_while_one_does_not_fit() {
+        let (w, ht) = (1086.0, 612.0);
+        let mut h = test_window::open(app(false), vec2(w, ht));
+        assert_eq!(test_window::panel_rect(&h, "tools").width(), column_width(2.0));
+        let visible = egui::Rect::from_min_max(pos2(0.0, 0.0), pos2(w, ht - STATUS_H));
+        for label in [LAST_TOOL, FILL] {
+            let r = rect(&h, label);
+            assert!(visible.contains_rect(r), "{label} at {r:?} is outside {visible:?} without scrolling");
+        }
+        assert!(!h.state().app.ui.tools_double_column);
+        // A taller window brings the single column back.
+        h.set_size(vec2(1400.0, 900.0));
+        h.run_steps(4);
+        assert_eq!(test_window::panel_rect(&h, "tools").width(), column_width(1.0));
+        assert!(!h.state().app.ui.tools_double_column);
+    }
+
+    #[test]
+    fn a_tall_window_keeps_one_column_and_does_not_scroll() {
+        let mut h = test_window::open(app(false), vec2(1400.0, 900.0));
+        let panel = test_window::panel_rect(&h, "tools");
+        assert_eq!(panel.width(), column_width(1.0));
+        let before = (rect(&h, LAST_TOOL), rect(&h, FILL));
+        assert!(panel.contains_rect(before.0) && panel.contains_rect(before.1), "{before:?} outside {panel:?}");
+        wheel(&mut h, panel.center(), vec2(0.0, -2000.0));
+        assert_eq!((rect(&h, LAST_TOOL), rect(&h, FILL)), before);
+    }
+}
diff --git a/crates/ui-egui/src/widgets.rs b/crates/ui-egui/src/widgets.rs
index 8e6b721..dd7f3d8 100644
--- a/crates/ui-egui/src/widgets.rs
+++ b/crates/ui-egui/src/widgets.rs
@@ -572,6 +572,21 @@ pub fn segmented(ui: &mut Ui, labels: &[&str], active: usize, width: f32) -> Opt
     out
 }
 
+/// Scrolling for a bar that a small window cuts off (Tools panel, Control panel, application
+/// bar): the mouse wheel scrolls the bar's only direction, and a thin scroll bar floats over the
+/// contents, so nothing moves and nothing shows while everything fits.
+pub fn overflow_scrolling(ui: &mut Ui) {
+    let style = ui.style_mut();
+    style.always_scroll_the_only_direction = true;
+    // A caption at the end of a scrolled row gets only what is left of it: extend, don't wrap.
+    style.wrap_mode = Some(egui::TextWrapMode::Extend);
+    let s = &mut style.spacing.scroll;
+    *s = egui::style::ScrollStyle::floating();
+    s.bar_width = 6.0;
+    // A faint handle while the pointer is elsewhere: the bar shows there is more.
+    s.dormant_handle_opacity = 0.5;
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;