Vercel MCP Adapter

mcp-handler is a framework-agnostic HTTP adapter for hosting Model Context Protocol (MCP) servers in JavaScript and TypeScript applications. It turns an MCP server definition into a Web-standard (Request) => Promise<Response> handler that can be mounted in Next.js, Nuxt/Nitro, SvelteKit, Hono, and other Fetch-compatible frameworks.

Built on MCP SDK v2, it serves the 2026-07-28 MCP specification natively while transparently falling back to stateless Streamable HTTP for 2025-era clients — one handler, both protocol generations.

Installation

npm install mcp-handler@^2 @modelcontextprotocol/server@^2 zod@^4

Note: mcp-handler 2.x requires the MCP SDK v2 packages (@modelcontextprotocol/server ^2.0.0), zod ^4.2.0, and Node.js 20+. If you're on @modelcontextprotocol/sdk 1.x, use mcp-handler 1.x.

Framework Compatibility

createMcpHandler returns a Web-standard request handler, so the package is not tied to Vercel or any particular framework. It can be mounted in:

• Next.js Route Handlers
• Nuxt/Nitro server handlers using fromWebHandler
• SvelteKit server routes
• Hono routes using c.req.raw
• Other frameworks that expose Fetch-compatible Request and Response APIs

Frameworks based on Node.js IncomingMessage and ServerResponse, such as Express, require a Web Request adapter or the official MCP framework middleware.

Quick Start (Next.js)

// app/api/mcp/route.ts
import { createMcpHandler } from "mcp-handler";
import { z } from "zod";

const handler = createMcpHandler((server) => {
  server.registerTool(
    "roll_dice",
    {
      title: "Roll Dice",
      description: "Roll a dice with a specified number of sides.",
      inputSchema: z.object({
        sides: z.number().int().min(2),
      }),
    },
    async ({ sides }) => {
      const value = 1 + Math.floor(Math.random() * sides);
      return {
        content: [{ type: "text", text: `🎲 You rolled a ${value}!` }],
      };
    },
  );
});

export { handler as GET, handler as POST };

/api/mcp is a convention, not a required path. mcp-handler does not inspect the request pathname, so you can place this handler at any framework route and give clients that route's complete URL.

Connecting Clients

If your client supports Streamable HTTP, connect directly:

{
  "remote-example": {
    "url": "http://localhost:3000/api/mcp"
  }
}

For stdio-only clients, use mcp-remote:

{
  "remote-example": {
    "command": "npx",
    "args": ["-y", "mcp-remote", "http://localhost:3000/api/mcp"]
  }
}

Protocol Support

• 2026-07-28 (current): served natively — stateless, no sessions, per-request _meta envelope, server/discover.
• 2025-era Streamable HTTP: served via the SDK's stateless legacy fallback from the same handler. GET/DELETE session operations answer 405 (serving is stateless).
• HTTP+SSE transport (2024-11-05): removed in 2.x. Mount only the Streamable HTTP handler; unmounted /sse and /message paths are handled by your framework. Redis is no longer needed or used.

Authorization (CIMD era)

The 2026-07-28 spec deprecates Dynamic Client Registration (DCR) in favor of Client ID Metadata Documents (CIMD), where the OAuth client identifies itself with an HTTPS URL that serves its metadata. CIMD support is advertised and implemented by your authorization server (client_id_metadata_document_supported in its RFC 8414 metadata); this package keeps your MCP server's resource-server surface up to date:

• withMcpAuth verifies bearer tokens and answers 401/403 with RFC 9728-compliant WWW-Authenticate challenges pointing at your protected resource metadata.
• protectedResourceHandler serves the RFC 9728 Protected Resource Metadata document listing your authorization servers.

See Authorization for wiring details.

Migrating from 1.x

• Install @modelcontextprotocol/server (v2) and zod@^4; remove @modelcontextprotocol/sdk and redis.
• inputSchema/argsSchema take a full Standard Schema (e.g. z.object({ ... })) instead of a raw zod shape.
• Variadic server.tool(...) / .prompt(...) / .resource(...) are removed — use registerTool / registerPrompt / registerResource.
• In handler callbacks, extra.authInfo is now ctx.http?.authInfo.
• createMcpHandler(initialize, serverOptions, config) is now createMcpHandler(initialize, options) — one options object combining the SDK's server options with serverInfo, verboseLogs, and onEvent.
• Route and transport config options from 1.x (basePath, streamableHttpEndpoint, sseEndpoint, sseMessageEndpoint, disableSse, redisUrl, maxDuration, and sessionIdGenerator) are removed. Mount the handler at the desired route instead.

Documentation

• Client Integration - Claude Desktop, Cursor, Windsurf setup
• Authorization - OAuth and token verification
• Advanced Usage - Dynamic routing, Nuxt, configuration options

Features

• Framework-agnostic: Web-standard Request and Response handler
• Framework compatibility: Next.js, Nuxt/Nitro, SvelteKit, Hono, and other Fetch-compatible frameworks
• Dual-era protocol support: 2026-07-28 (stateless) and 2025-era Streamable HTTP from one handler
• TypeScript Support: Full type definitions included

Requirements

• Node.js 20+
• A framework with Web-standard Request and Response APIs, either directly or through an adapter
• Next.js 13+ when using Next.js, or Nuxt 3+ when using Nuxt

License

Apache-2.0