diff --git a/crates/voltex_editor/src/dock.rs b/crates/voltex_editor/src/dock.rs
new file mode 100644
index 0000000..f757b70
--- /dev/null
+++ b/crates/voltex_editor/src/dock.rs
@@ -0,0 +1,263 @@
+const TAB_BAR_HEIGHT: f32 = 20.0;
+const MIN_RATIO: f32 = 0.1;
+const MAX_RATIO: f32 = 0.9;
+const RESIZE_HANDLE_HALF: f32 = 3.0;
+const GLYPH_W: f32 = 8.0;
+const TAB_PADDING: f32 = 8.0;
+
+#[derive(Clone, Copy, Debug)]
+pub struct Rect {
+    pub x: f32,
+    pub y: f32,
+    pub w: f32,
+    pub h: f32,
+}
+
+impl Rect {
+    pub fn contains(&self, px: f32, py: f32) -> bool {
+        px >= self.x && px < self.x + self.w && py >= self.y && py < self.y + self.h
+    }
+}
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum Axis {
+    Horizontal,
+    Vertical,
+}
+
+pub enum DockNode {
+    Leaf { tabs: Vec<u32>, active: usize },
+    Split { axis: Axis, ratio: f32, children: [Box<DockNode>; 2] },
+}
+
+impl DockNode {
+    pub fn leaf(tabs: Vec<u32>) -> Self {
+        DockNode::Leaf { tabs, active: 0 }
+    }
+
+    pub fn split(axis: Axis, ratio: f32, a: DockNode, b: DockNode) -> Self {
+        DockNode::Split {
+            axis,
+            ratio: ratio.clamp(MIN_RATIO, MAX_RATIO),
+            children: [Box::new(a), Box::new(b)],
+        }
+    }
+}
+
+pub struct LeafLayout {
+    pub leaf_index: usize,
+    pub tabs: Vec<u32>,
+    pub active: usize,
+    pub tab_bar_rect: Rect,
+    pub content_rect: Rect,
+}
+
+struct SplitLayout {
+    rect: Rect,
+    axis: Axis,
+    boundary: f32,
+    path: Vec<usize>,
+}
+
+struct ResizeState {
+    path: Vec<usize>,
+    axis: Axis,
+    origin: f32,
+    size: f32,
+}
+
+pub struct DockTree {
+    root: DockNode,
+    names: Vec<&'static str>,
+    cached_leaves: Vec<LeafLayout>,
+    cached_splits: Vec<SplitLayout>,
+    resizing: Option<ResizeState>,
+    prev_mouse_down: bool,
+}
+
+fn layout_recursive(
+    node: &DockNode,
+    rect: Rect,
+    path: &mut Vec<usize>,
+    leaf_counter: &mut usize,
+    leaves: &mut Vec<LeafLayout>,
+    splits: &mut Vec<SplitLayout>,
+) {
+    match node {
+        DockNode::Leaf { tabs, active } => {
+            debug_assert!(!tabs.is_empty(), "DockNode::Leaf must have at least one tab");
+            let idx = *leaf_counter;
+            *leaf_counter += 1;
+            leaves.push(LeafLayout {
+                leaf_index: idx,
+                tabs: tabs.clone(),
+                active: (*active).min(tabs.len() - 1),
+                tab_bar_rect: Rect { x: rect.x, y: rect.y, w: rect.w, h: TAB_BAR_HEIGHT },
+                content_rect: Rect {
+                    x: rect.x,
+                    y: rect.y + TAB_BAR_HEIGHT,
+                    w: rect.w,
+                    h: (rect.h - TAB_BAR_HEIGHT).max(0.0),
+                },
+            });
+        }
+        DockNode::Split { axis, ratio, children } => {
+            let (r1, r2, boundary) = match axis {
+                Axis::Horizontal => {
+                    let w1 = rect.w * ratio;
+                    let b = rect.x + w1;
+                    (
+                        Rect { x: rect.x, y: rect.y, w: w1, h: rect.h },
+                        Rect { x: b, y: rect.y, w: rect.w - w1, h: rect.h },
+                        b,
+                    )
+                }
+                Axis::Vertical => {
+                    let h1 = rect.h * ratio;
+                    let b = rect.y + h1;
+                    (
+                        Rect { x: rect.x, y: rect.y, w: rect.w, h: h1 },
+                        Rect { x: rect.x, y: b, w: rect.w, h: rect.h - h1 },
+                        b,
+                    )
+                }
+            };
+            splits.push(SplitLayout { rect, axis: *axis, boundary, path: path.clone() });
+            path.push(0);
+            layout_recursive(&children[0], r1, path, leaf_counter, leaves, splits);
+            path.pop();
+            path.push(1);
+            layout_recursive(&children[1], r2, path, leaf_counter, leaves, splits);
+            path.pop();
+        }
+    }
+}
+
+impl DockTree {
+    pub fn new(root: DockNode, names: Vec<&'static str>) -> Self {
+        DockTree {
+            root,
+            names,
+            cached_leaves: Vec::new(),
+            cached_splits: Vec::new(),
+            resizing: None,
+            prev_mouse_down: false,
+        }
+    }
+
+    pub fn layout(&mut self, rect: Rect) -> Vec<(u32, Rect)> {
+        self.cached_leaves.clear();
+        self.cached_splits.clear();
+        let mut path = Vec::new();
+        let mut counter = 0;
+        layout_recursive(
+            &self.root,
+            rect,
+            &mut path,
+            &mut counter,
+            &mut self.cached_leaves,
+            &mut self.cached_splits,
+        );
+        self.cached_leaves
+            .iter()
+            .map(|l| {
+                let active = l.active.min(l.tabs.len().saturating_sub(1));
+                (l.tabs[active], l.content_rect)
+            })
+            .collect()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_rect_contains() {
+        let r = Rect { x: 10.0, y: 20.0, w: 100.0, h: 50.0 };
+        assert!(r.contains(50.0, 40.0));
+        assert!(!r.contains(5.0, 40.0));
+        assert!(!r.contains(50.0, 80.0));
+    }
+
+    #[test]
+    fn test_layout_single_leaf() {
+        let mut dock = DockTree::new(DockNode::leaf(vec![0]), vec!["Panel0"]);
+        let areas = dock.layout(Rect { x: 0.0, y: 0.0, w: 400.0, h: 300.0 });
+        assert_eq!(areas.len(), 1);
+        assert_eq!(areas[0].0, 0);
+        let r = &areas[0].1;
+        assert!((r.y - 20.0).abs() < 1e-3);
+        assert!((r.h - 280.0).abs() < 1e-3);
+    }
+
+    #[test]
+    fn test_layout_horizontal_split() {
+        let mut dock = DockTree::new(
+            DockNode::split(Axis::Horizontal, 0.25, DockNode::leaf(vec![0]), DockNode::leaf(vec![1])),
+            vec!["Left", "Right"],
+        );
+        let areas = dock.layout(Rect { x: 0.0, y: 0.0, w: 400.0, h: 300.0 });
+        assert_eq!(areas.len(), 2);
+        let left = areas.iter().find(|(id, _)| *id == 0).unwrap();
+        assert!((left.1.w - 100.0).abs() < 1e-3);
+        let right = areas.iter().find(|(id, _)| *id == 1).unwrap();
+        assert!((right.1.w - 300.0).abs() < 1e-3);
+    }
+
+    #[test]
+    fn test_layout_vertical_split() {
+        let mut dock = DockTree::new(
+            DockNode::split(Axis::Vertical, 0.5, DockNode::leaf(vec![0]), DockNode::leaf(vec![1])),
+            vec!["Top", "Bottom"],
+        );
+        let areas = dock.layout(Rect { x: 0.0, y: 0.0, w: 400.0, h: 300.0 });
+        let top = areas.iter().find(|(id, _)| *id == 0).unwrap();
+        assert!((top.1.h - 130.0).abs() < 1e-3);
+    }
+
+    #[test]
+    fn test_layout_nested_split() {
+        let mut dock = DockTree::new(
+            DockNode::split(
+                Axis::Horizontal,
+                0.25,
+                DockNode::leaf(vec![0]),
+                DockNode::split(Axis::Vertical, 0.5, DockNode::leaf(vec![1]), DockNode::leaf(vec![2])),
+            ),
+            vec!["A", "B", "C"],
+        );
+        let areas = dock.layout(Rect { x: 0.0, y: 0.0, w: 400.0, h: 300.0 });
+        assert_eq!(areas.len(), 3);
+    }
+
+    #[test]
+    fn test_layout_active_tab_only() {
+        let mut dock = DockTree::new(
+            DockNode::Leaf { tabs: vec![0, 1, 2], active: 1 },
+            vec!["A", "B", "C"],
+        );
+        let areas = dock.layout(Rect { x: 0.0, y: 0.0, w: 400.0, h: 300.0 });
+        assert_eq!(areas[0].0, 1);
+    }
+
+    #[test]
+    fn test_active_clamped_if_out_of_bounds() {
+        let mut dock = DockTree::new(
+            DockNode::Leaf { tabs: vec![0], active: 5 },
+            vec!["A"],
+        );
+        let areas = dock.layout(Rect { x: 0.0, y: 0.0, w: 400.0, h: 300.0 });
+        assert_eq!(areas[0].0, 0);
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_empty_tabs_panics() {
+        let mut dock = DockTree::new(
+            DockNode::Leaf { tabs: vec![], active: 0 },
+            vec![],
+        );
+        dock.layout(Rect { x: 0.0, y: 0.0, w: 400.0, h: 300.0 });
+    }
+}
diff --git a/crates/voltex_editor/src/lib.rs b/crates/voltex_editor/src/lib.rs
index b5ec6e9..fd09350 100644
--- a/crates/voltex_editor/src/lib.rs
+++ b/crates/voltex_editor/src/lib.rs
@@ -4,9 +4,11 @@ pub mod layout;
 pub mod renderer;
 pub mod ui_context;
 pub mod widgets;
+pub mod dock;
 
 pub use font::FontAtlas;
 pub use draw_list::{DrawVertex, DrawCommand, DrawList};
 pub use layout::LayoutState;
 pub use renderer::UiRenderer;
 pub use ui_context::UiContext;
+pub use dock::{DockTree, DockNode, Axis, Rect, LeafLayout};