diff --git a/README.md b/README.md
index 2f92598..57075f7 100644
--- a/README.md
+++ b/README.md
@@ -23,6 +23,11 @@ Open:
 - Health: `http://localhost:8787/health`
 - MCP UI bundle descriptor: `http://localhost:8787/mcp/ui-bundle`
 
+Version metadata:
+- REST and MCP tool responses include `api_version` and `schema_version`.
+- Current values: `api_version=0.3.0`, `schema_version=1.0.0`.
+- Compatibility policy (current): additive, backward-compatible fields may be introduced in the same API minor version.
+
 ## REST API
 
 ### `POST /compile`
diff --git a/src/mcp-server.js b/src/mcp-server.js
index d592de7..5c0444b 100644
--- a/src/mcp-server.js
+++ b/src/mcp-server.js
@@ -1,4 +1,6 @@
 import { compile, analyze } from "./compile.js";
+const API_VERSION = "0.3.0";
+const SCHEMA_VERSION = "1.0.0";
 
 const SERVER_INFO = {
   name: "schemeta-mcp",
@@ -87,10 +89,20 @@ function toolListResult() {
   };
 }
 
+function withEnvelopeMeta(payload) {
+  return {
+    api_version: API_VERSION,
+    schema_version: SCHEMA_VERSION,
+    ...payload
+  };
+}
+
 function uiBundleDescriptor() {
   return {
     name: "schemeta-workspace",
     version: "0.2.0",
+    api_version: API_VERSION,
+    schema_version: SCHEMA_VERSION,
     entry: "/",
     title: "Schemeta Workspace",
     transport: "iframe"
@@ -104,7 +116,7 @@ function handleToolCall(name, args) {
 
   if (name === "schemeta_compile") {
     const payload = decodePayload(args.payload);
-    const result = compile(payload, args.options ?? {});
+    const result = withEnvelopeMeta(compile(payload, args.options ?? {}));
     return {
       content: [{ type: "text", text: JSON.stringify(result) }],
       structuredContent: result,
@@ -114,7 +126,7 @@ function handleToolCall(name, args) {
 
   if (name === "schemeta_analyze") {
     const payload = decodePayload(args.payload);
-    const result = analyze(payload, args.options ?? {});
+    const result = withEnvelopeMeta(analyze(payload, args.options ?? {}));
     return {
       content: [{ type: "text", text: JSON.stringify(result) }],
       structuredContent: result,
diff --git a/src/server.js b/src/server.js
index 63b9314..c383174 100644
--- a/src/server.js
+++ b/src/server.js
@@ -9,6 +9,8 @@ const PORT = Number(process.env.PORT ?? "8787");
 const MAX_BODY_BYTES = Number(process.env.MAX_BODY_BYTES ?? 2 * 1024 * 1024);
 const CORS_ORIGIN = process.env.CORS_ORIGIN ?? "*";
 const FRONTEND_ROOT = join(process.cwd(), "frontend");
+const API_VERSION = "0.3.0";
+const SCHEMA_VERSION = "1.0.0";
 
 const MIME_TYPES = {
   ".html": "text/html; charset=utf-8",
@@ -123,6 +125,14 @@ function parsePayloadOptions(body) {
   };
 }
 
+function withEnvelopeMeta(payload) {
+  return {
+    api_version: API_VERSION,
+    schema_version: SCHEMA_VERSION,
+    ...payload
+  };
+}
+
 const server = createServer(async (req, res) => {
   if (!req.url || !req.method) {
     return json(res, 400, errorEnvelope("invalid_request", "Invalid request."));
@@ -141,6 +151,8 @@ const server = createServer(async (req, res) => {
     return json(res, 200, {
       ok: true,
       service: "schemeta",
+      api_version: API_VERSION,
+      schema_version: SCHEMA_VERSION,
       status: "ok",
       date: new Date().toISOString()
     });
@@ -151,6 +163,8 @@ const server = createServer(async (req, res) => {
       ok: true,
       name: "schemeta-workspace",
       version: "0.2.0",
+      api_version: API_VERSION,
+      schema_version: SCHEMA_VERSION,
       entry: "/",
       title: "Schemeta Workspace",
       transport: "iframe"
@@ -161,7 +175,7 @@ const server = createServer(async (req, res) => {
     try {
       const body = await readBody(req);
       const parsed = parsePayloadOptions(body);
-      return json(res, 200, analyze(parsed.payload, parsed.options));
+      return json(res, 200, withEnvelopeMeta(analyze(parsed.payload, parsed.options)));
     } catch (err) {
       if (err?.code === "PAYLOAD_TOO_LARGE") {
         return json(res, 413, errorEnvelope("payload_too_large", `Request body exceeds ${MAX_BODY_BYTES} bytes.`));
@@ -177,7 +191,7 @@ const server = createServer(async (req, res) => {
     try {
       const body = await readBody(req);
       const parsed = parsePayloadOptions(body);
-      return json(res, 200, compile(parsed.payload, parsed.options));
+      return json(res, 200, withEnvelopeMeta(compile(parsed.payload, parsed.options)));
     } catch (err) {
       if (err?.code === "PAYLOAD_TOO_LARGE") {
         return json(res, 413, errorEnvelope("payload_too_large", `Request body exceeds ${MAX_BODY_BYTES} bytes.`));
@@ -198,8 +212,10 @@ const server = createServer(async (req, res) => {
       const laidOut = applyLayoutToModel(model, { respectLocks: false });
       return json(res, 200, {
         ok: true,
+        api_version: API_VERSION,
+        schema_version: SCHEMA_VERSION,
         model: laidOut,
-        compile: compile(laidOut, parsed.options)
+        compile: withEnvelopeMeta(compile(laidOut, parsed.options))
       });
     } catch (err) {
       if (err?.code === "PAYLOAD_TOO_LARGE") {
@@ -221,8 +237,10 @@ const server = createServer(async (req, res) => {
       const laidOut = applyLayoutToModel(model, { respectLocks: true });
       return json(res, 200, {
         ok: true,
+        api_version: API_VERSION,
+        schema_version: SCHEMA_VERSION,
         model: laidOut,
-        compile: compile(laidOut, parsed.options)
+        compile: withEnvelopeMeta(compile(laidOut, parsed.options))
       });
     } catch (err) {
       if (err?.code === "PAYLOAD_TOO_LARGE") {