diff --git a/src/parser/schema.test.ts b/src/parser/schema.test.ts
new file mode 100644
index 00000000..12db24b6
--- /dev/null
+++ b/src/parser/schema.test.ts
@@ -0,0 +1,116 @@
+import assert from "node:assert/strict";
+import { describe, it } from "vitest";
+import { z } from "zod";
+import { validateProseMirrorDocument, collectNodeTypes, collectMarkTypes } from "./schema.js";
+
+describe("validateProseMirrorDocument", () => {
+  it("passes when valid root node (type: 'doc') is provided", () => {
+    const doc = { type: "doc" };
+    const result = validateProseMirrorDocument(doc);
+    assert.deepEqual(result, doc);
+  });
+
+  it("throws ZodError when invalid root node is provided", () => {
+    const doc = { type: "paragraph" };
+    assert.throws(() => validateProseMirrorDocument(doc), z.ZodError);
+  });
+
+  it("throws ZodError when type is missing", () => {
+    const doc = { attrs: {} };
+    assert.throws(() => validateProseMirrorDocument(doc), z.ZodError);
+  });
+
+  it("validates nested content properly", () => {
+    const doc = {
+      type: "doc",
+      content: [
+        {
+          type: "paragraph",
+          content: [
+            {
+              type: "text",
+              text: "Hello World",
+              marks: [{ type: "bold" }],
+            },
+          ],
+        },
+      ],
+    };
+    const result = validateProseMirrorDocument(doc);
+    assert.deepEqual(result, doc);
+  });
+
+  it("throws ZodError when nested content is invalid", () => {
+    const doc = {
+      type: "doc",
+      content: [
+        {
+          type: "paragraph",
+          content: [
+            {
+              text: "Hello World",
+              marks: [{ type: "bold" }],
+            },
+          ],
+        },
+      ],
+    };
+    assert.throws(() => validateProseMirrorDocument(doc), z.ZodError);
+  });
+});
+
+describe("collectNodeTypes", () => {
+  it("collects unique node types in alphabetical order", () => {
+    const doc = {
+      type: "doc",
+      content: [
+        {
+          type: "paragraph",
+          content: [{ type: "text" }, { type: "text" }],
+        },
+        {
+          type: "heading",
+        },
+        {
+          type: "paragraph",
+        },
+      ],
+    };
+    const result = collectNodeTypes(doc);
+    assert.deepEqual(result, ["doc", "heading", "paragraph", "text"]);
+  });
+});
+
+describe("collectMarkTypes", () => {
+  it("collects unique mark types in alphabetical order", () => {
+    const doc = {
+      type: "doc",
+      content: [
+        {
+          type: "paragraph",
+          content: [
+            {
+              type: "text",
+              marks: [{ type: "italic" }, { type: "bold" }],
+            },
+            {
+              type: "text",
+              marks: [{ type: "bold" }],
+            },
+          ],
+        },
+        {
+          type: "heading",
+          content: [
+            {
+              type: "text",
+              marks: [{ type: "strike" }],
+            },
+          ],
+        },
+      ],
+    };
+    const result = collectMarkTypes(doc);
+    assert.deepEqual(result, ["bold", "italic", "strike"]);
+  });
+});