diff --git a/crates/oxide_kernel/src/lib.rs b/crates/oxide_kernel/src/lib.rs
index a35e2c20..21252791 100644
--- a/crates/oxide_kernel/src/lib.rs
+++ b/crates/oxide_kernel/src/lib.rs
@@ -1,3 +1,4 @@
 #![doc = "OxideJS - Shared kernel (CodeForge, ShapeForge, IcForge, StringForge, BuiltinWorld)"]
 
+pub mod shape_forge;
 pub mod string_forge;
diff --git a/crates/oxide_kernel/src/shape_forge.rs b/crates/oxide_kernel/src/shape_forge.rs
new file mode 100644
index 00000000..2a453b52
--- /dev/null
+++ b/crates/oxide_kernel/src/shape_forge.rs
@@ -0,0 +1,255 @@
+use std::sync::atomic::{AtomicU32, Ordering};
+use std::sync::{Arc, RwLock};
+
+use dashmap::DashMap;
+
+pub type ShapeId = u32;
+pub type StringIndex = u32;
+
+pub const EMPTY_SHAPE_ID: ShapeId = 1;
+const EMPTY_SENTINEL: StringIndex = u32::MAX;
+
+#[derive(Debug, Clone)]
+pub struct Shape {
+    pub id: ShapeId,
+    pub property_name: StringIndex,
+    pub property_offset: u8,
+    pub parent: Option<ShapeId>,
+}
+
+pub struct ShapeForge {
+    shapes: RwLock<Vec<Option<Arc<Shape>>>>,
+    transitions: DashMap<u64, ShapeId>,
+    next_id: AtomicU32,
+}
+
+impl ShapeForge {
+    pub fn new() -> Self {
+        let forge = Self {
+            shapes: RwLock::new(Vec::with_capacity(256)),
+            transitions: DashMap::with_capacity(256),
+            next_id: AtomicU32::new(2),
+        };
+        {
+            let mut shapes = forge.shapes.write().unwrap();
+            let empty = Arc::new(Shape {
+                id: EMPTY_SHAPE_ID,
+                property_name: EMPTY_SENTINEL,
+                property_offset: 0,
+                parent: None,
+            });
+            debug_assert_eq!(shapes.len(), 0);
+            shapes.push(Some(empty));
+        }
+        forge
+    }
+
+    pub fn pack_key(parent_id: ShapeId, prop_name: StringIndex) -> u64 {
+        ((parent_id as u64) << 32) | (prop_name as u64)
+    }
+
+    fn compute_offset_inner(shape_id: ShapeId, shapes: &[Option<Arc<Shape>>]) -> u8 {
+        let mut count = 0u8;
+        let mut cursor = Some(shape_id);
+        while let Some(id) = cursor {
+            match shapes.get((id - 1) as usize).and_then(|s| s.clone()) {
+                Some(s) => {
+                    if s.property_name != EMPTY_SENTINEL {
+                        count += 1;
+                    }
+                    cursor = s.parent;
+                }
+                None => break,
+            }
+        }
+        count.min(31)
+    }
+
+    pub fn make_shape(&self, parent_id: ShapeId, prop_name: StringIndex) -> ShapeId {
+        let key = Self::pack_key(parent_id, prop_name);
+
+        if let Some(entry) = self.transitions.get(&key) {
+            return *entry;
+        }
+
+        let shapes_read = self.shapes.read().unwrap();
+        let prop_offset = Self::compute_offset_inner(parent_id, &shapes_read);
+        drop(shapes_read);
+
+        let new_id = self.next_id.fetch_add(1, Ordering::Relaxed);
+
+        let shape = Arc::new(Shape {
+            id: new_id,
+            property_name: prop_name,
+            property_offset: prop_offset,
+            parent: Some(parent_id),
+        });
+
+        {
+            let mut shapes = self.shapes.write().unwrap();
+            while shapes.len() < new_id as usize {
+                shapes.push(None);
+            }
+            shapes[(new_id - 1) as usize] = Some(shape);
+        }
+
+        *self.transitions.entry(key).or_insert(new_id).value()
+    }
+
+    pub fn get_shape(&self, id: ShapeId) -> Option<Arc<Shape>> {
+        let shapes = self.shapes.read().unwrap();
+        shapes.get((id - 1) as usize).and_then(|s| s.clone())
+    }
+
+    pub fn lookup_offset(&self, shape_id: ShapeId, prop_name: StringIndex) -> Option<u8> {
+        let shapes = self.shapes.read().unwrap();
+        let mut cursor = Some(shape_id);
+        while let Some(id) = cursor {
+            match shapes.get((id - 1) as usize).and_then(|s| s.clone()) {
+                Some(s) => {
+                    if s.property_name == prop_name && s.property_name != EMPTY_SENTINEL {
+                        return Some(s.property_offset);
+                    }
+                    cursor = s.parent;
+                }
+                None => return None,
+            }
+        }
+        None
+    }
+
+    pub fn shape_prop_count(&self, shape_id: ShapeId) -> u8 {
+        let shapes = self.shapes.read().unwrap();
+        let mut count = 0u8;
+        let mut cursor = Some(shape_id);
+        while let Some(id) = cursor {
+            match shapes.get((id - 1) as usize).and_then(|s| s.clone()) {
+                Some(s) => {
+                    if s.property_name != EMPTY_SENTINEL {
+                        count += 1;
+                    }
+                    cursor = s.parent;
+                }
+                None => break,
+            }
+        }
+        count
+    }
+}
+
+impl Default for ShapeForge {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::sync::Barrier;
+
+    #[test]
+    fn empty_shape_exists() {
+        let forge = ShapeForge::new();
+        let s = forge.get_shape(EMPTY_SHAPE_ID);
+        assert!(s.is_some());
+        let s = s.unwrap();
+        assert_eq!(s.id, EMPTY_SHAPE_ID);
+        assert!(s.parent.is_none());
+    }
+
+    #[test]
+    fn make_shape_creates_new_id() {
+        let forge = ShapeForge::new();
+        let key: StringIndex = 1_000_000;
+        let s1 = forge.make_shape(EMPTY_SHAPE_ID, key);
+        assert!(s1 > EMPTY_SHAPE_ID);
+        let shape = forge.get_shape(s1).unwrap();
+        assert_eq!(shape.property_name, key);
+        assert_eq!(shape.parent, Some(EMPTY_SHAPE_ID));
+    }
+
+    #[test]
+    fn hash_cons_returns_same_id() {
+        let forge = ShapeForge::new();
+        let key: StringIndex = 1_000_001;
+        let a = forge.make_shape(EMPTY_SHAPE_ID, key);
+        let b = forge.make_shape(EMPTY_SHAPE_ID, key);
+        assert_eq!(a, b);
+    }
+
+    #[test]
+    fn different_props_different_ids() {
+        let forge = ShapeForge::new();
+        let a = forge.make_shape(EMPTY_SHAPE_ID, 1_000_002);
+        let b = forge.make_shape(EMPTY_SHAPE_ID, 1_000_003);
+        assert_ne!(a, b);
+    }
+
+    #[test]
+    fn chain_of_three() {
+        let forge = ShapeForge::new();
+        let s1 = forge.make_shape(EMPTY_SHAPE_ID, 1_000_010);
+        let s2 = forge.make_shape(s1, 1_000_020);
+        let s3 = forge.make_shape(s2, 1_000_030);
+
+        assert_eq!(forge.shape_prop_count(s3), 3);
+
+        assert_eq!(forge.lookup_offset(s3, 1_000_030), Some(2));
+        assert_eq!(forge.lookup_offset(s3, 1_000_020), Some(1));
+        assert_eq!(forge.lookup_offset(s3, 1_000_010), Some(0));
+        assert_eq!(forge.lookup_offset(s3, 99), None);
+    }
+
+    #[test]
+    fn two_branches_share_ancestor() {
+        let forge = ShapeForge::new();
+        let base = forge.make_shape(EMPTY_SHAPE_ID, 1_000_040);
+        let branch_a = forge.make_shape(base, 1_000_050);
+        let branch_b = forge.make_shape(base, 1_000_060);
+        assert_ne!(branch_a, branch_b);
+        let a_shape = forge.get_shape(branch_a).unwrap();
+        let b_shape = forge.get_shape(branch_b).unwrap();
+        assert_eq!(a_shape.parent, Some(base));
+        assert_eq!(b_shape.parent, Some(base));
+    }
+
+    #[test]
+    fn edge_same_structure_different_names() {
+        let forge = ShapeForge::new();
+        let s1 = forge.make_shape(EMPTY_SHAPE_ID, 1_000_070);
+        let s2 = forge.make_shape(s1, 1_000_080);
+        let s3 = forge.make_shape(EMPTY_SHAPE_ID, 1_000_090);
+        let s4 = forge.make_shape(s3, 1_000_100);
+        assert_ne!(s1, s3);
+        assert_ne!(s2, s4);
+        assert_eq!(forge.lookup_offset(s2, 1_000_070), Some(0));
+        assert_eq!(forge.lookup_offset(s4, 1_000_090), Some(0));
+    }
+
+    #[test]
+    fn concurrent_make_same_key() {
+        let forge = Arc::new(ShapeForge::new());
+        let key: StringIndex = 1_000_200;
+        let barrier = Arc::new(Barrier::new(2));
+
+        let f1 = Arc::clone(&forge);
+        let b1 = Arc::clone(&barrier);
+        let h1 = std::thread::spawn(move || {
+            b1.wait();
+            f1.make_shape(EMPTY_SHAPE_ID, key)
+        });
+
+        let f2 = Arc::clone(&forge);
+        let b2 = Arc::clone(&barrier);
+        let h2 = std::thread::spawn(move || {
+            b2.wait();
+            f2.make_shape(EMPTY_SHAPE_ID, key)
+        });
+
+        let id1 = h1.join().unwrap();
+        let id2 = h2.join().unwrap();
+        assert_eq!(id1, id2);
+        assert!(id1 > EMPTY_SHAPE_ID);
+    }
+}