Add jsonLimit option to createMcpExpressApp (#1625)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Konstantin Konstantinov <KKonstantinov@users.noreply.github.com>

Author: 3 people

.changeset/twelve-dodos-taste.md

@@ -0,0 +1,5 @@
+---
+"@modelcontextprotocol/express": patch
+---
+
+Add jsonLimit option to createMcpExpressApp

packages/middleware/express/src/express.ts

@@ -22,6 +22,15 @@ export interface CreateMcpExpressAppOptions {
      * to restrict which hostnames are allowed.
      */
     allowedHosts?: string[];
+
+    /**
+     * Controls the maximum request body size for the JSON body parser.
+     * Passed directly to Express's `express.json({ limit })` option.
+     * Defaults to Express's built-in default of `'100kb'`.
+     *
+     * @example '1mb', '500kb', '10mb'
+     */
+    jsonLimit?: string;
 }
 
 /**
@@ -51,10 +60,10 @@ export interface CreateMcpExpressAppOptions {
  * ```
  */
 export function createMcpExpressApp(options: CreateMcpExpressAppOptions = {}): Express {
-    const { host = '127.0.0.1', allowedHosts } = options;
+    const { host = '127.0.0.1', allowedHosts, jsonLimit } = options;
 
     const app = express();
-    app.use(express.json());
+    app.use(express.json(jsonLimit ? { limit: jsonLimit } : undefined));
 
     // If allowedHosts is explicitly provided, use that for validation
     if (allowedHosts) {

packages/middleware/express/test/express.test.ts

@@ -178,5 +178,15 @@ describe('@modelcontextprotocol/express', () => {
 
             warn.mockRestore();
         });
+
+        test('should accept jsonLimit option', () => {
+            const app = createMcpExpressApp({ jsonLimit: '10mb' });
+            expect(app).toBeDefined();
+        });
+
+        test('should work without jsonLimit option', () => {
+            const app = createMcpExpressApp();
+            expect(app).toBeDefined();
+        });
     });
 });