diff --git a/src/core/h.ts b/src/core/h.ts
index b18cec9..10900ec 100644
--- a/src/core/h.ts
+++ b/src/core/h.ts
@@ -3,7 +3,8 @@ import type { UNode, UElement, URoot, UType, UComponent, UniversalProps } from "
 let _idCounter = 0;
 
 export function h(type: UType, props?: UniversalProps | null, ...children: UNode[]): UElement | URoot {
-  const resolvedProps: UniversalProps = props ? { ...props } : {};
+  const { key, ...restProps } = props ?? {};
+  const resolvedProps: UniversalProps = restProps;
   const flatChildren = children.flat(Infinity as 1).filter((c: UNode) => c != null && c !== false) as UNode[];
 
   if (type === "root") {
@@ -18,6 +19,7 @@ export function h(type: UType, props?: UniversalProps | null, ...children: UNode
     type: type as string,
     props: resolvedProps,
     children: flatChildren,
+    ...(key != null ? { key: key as string } : {}),
   } as UElement;
 }
 
diff --git a/src/core/schema.ts b/src/core/schema.ts
index 4c060a6..59ee1ae 100644
--- a/src/core/schema.ts
+++ b/src/core/schema.ts
@@ -23,6 +23,7 @@ export const UJSX = Type.Module({
     type: Type.String(),
     props: Type.Ref("UniversalProps"),
     children: Type.Array(Type.Ref("UNode")),
+    key: Type.Optional(Type.String()),
   }),
 
   URoot: Type.Object({
@@ -45,6 +46,7 @@ export type UElement = {
   type: string;
   props: UniversalProps;
   children: UNode[];
+  key?: string;
 };
 export type URoot = {
   type: "root";
diff --git a/test/mod.test.ts b/test/mod.test.ts
index 4da727c..50f5856 100644
--- a/test/mod.test.ts
+++ b/test/mod.test.ts
@@ -1,7 +1,8 @@
 import { describe, it, expect } from "vitest";
 import { h, createRoot, createComponent, Fragment, jsx, jsxs, jsxDEV } from "../src/core/h.js";
-import { isUElement, isURoot, isUPrimitive } from "../src/core/schema.js";
+import { isUElement, isURoot, isUPrimitive, UJSX } from "../src/core/schema.js";
 import type { UNode, UElement } from "../src/core/schema.js";
+import { Value } from "@alkdev/typebox/value";
 import { Context } from "../src/core/context.js";
 import { TransformRegistry, childCtx, ctx as transformCtx } from "../src/transform/registry.js";
 import type { Direction } from "../src/core/context.js";
@@ -98,6 +99,60 @@ describe("type guards", () => {
   });
 });
 
+describe("UElement key field", () => {
+  it("h() extracts key from props and promotes to element level", () => {
+    const el = h("div", { key: "item-1", class: "test" }, "hello");
+    expect(isUElement(el)).toBe(true);
+    if (isUElement(el)) {
+      expect(el.key).toBe("item-1");
+      expect(el.props.key).toBeUndefined();
+      expect(el.props.class).toBe("test");
+    }
+  });
+
+  it("h() without key does not add key field", () => {
+    const el = h("div", { class: "test" }, "hello");
+    expect(isUElement(el)).toBe(true);
+    if (isUElement(el)) {
+      expect(el.key).toBeUndefined();
+    }
+  });
+
+  it("h() with null props has no key", () => {
+    const el = h("div", null, "hello");
+    expect(isUElement(el)).toBe(true);
+    if (isUElement(el)) {
+      expect(el.key).toBeUndefined();
+    }
+  });
+
+  it("UElement with key validates against TypeBox schema", () => {
+    const UElementSchema = UJSX.Import("UElement");
+    const el = h("li", { key: "a" }, "item");
+    expect(Value.Check(UElementSchema, el)).toBe(true);
+  });
+
+  it("UElement without key validates against TypeBox schema (backward compat)", () => {
+    const UElementSchema = UJSX.Import("UElement");
+    const el = h("li", { class: "item" }, "item");
+    expect(Value.Check(UElementSchema, el)).toBe(true);
+  });
+
+  it("URoot does not have a key field", () => {
+    const root = createRoot("r");
+    expect("key" in root).toBe(false);
+  });
+
+  it("h() with root type does not promote key to URoot", () => {
+    const root = h("root", { key: "should-not-appear", id: "test" }, "child");
+    expect(isURoot(root)).toBe(true);
+    if (isURoot(root)) {
+      expect("key" in root).toBe(false);
+      expect(root.props.key).toBeUndefined();
+    }
+  });
+});
+
 describe("Context", () => {
   it("stores and updates values", () => {
     const ctx = new Context({ density: "full", target: "markdown" });