Zero MCP

Zero-boilerplate HTTP MCP server toolkit. Skip the weight of @modelcontextprotocol/sdk and start shipping MCP tools in minutes.

Why Zero MCP instead of the official SDK?

The official @modelcontextprotocol/sdk ships with significant overhead—both in dependencies and performance—while implementing features most developers never use and missing critical conveniences. Zero MCP takes the opposite approach: minimal dependencies, faster cold starts, and ergonomics that get you shipping in minutes.

What's wrong with the official SDK?

• Dependency bloat – Bundles 12+ packages (Express, CORS middleware, rate limiting, EventSource polyfills, PKCE utilities) even for simple tool servers
• Performance overhead – Express-based transport stack adds latency and memory footprint versus native node:http
• Boilerplate hell – Requires manual Express app setup, transport wiring, session management, and schema registration for every server
• Missing conveniences – No Zod integration, no built-in lifecycle hooks, no automatic JSON Schema generation
• Feature bloat – Ships stdio transports, SSE streaming, client implementations, and auth flows that 80% of tool servers never touch

What Zero MCP delivers instead:

• 2 dependencies total – Just zod and zod-to-json-schema; nothing else pollutes your node_modules
• Native performance – Built-in node:http server with zero middleware overhead; ideal for serverless and edge runtimes
• Instant start – Instantiate McpServer, register tools, call start()—no Express config or transport plumbing
• Zod-first schemas – Define tool inputs with Zod; JSON Schema generation happens automatically
• Built-in observability – Lifecycle hooks for connections, tool calls, and errors work out of the box
• Production-ready CORS – Spec-aligned origin validation included for browser MCP clients
• Focused scope – Does one thing well: MCP tools over HTTP

Choose the official SDK if you need the full MCP spec (stdio transports, prompts API, auth flows). Choose Zero MCP when you want a fast, lean tool server without the baggage.

Installation

npm install zero-mcp zod

zero-mcp re-exports z, but keeping an explicit zod dependency avoids bundler surprises.

Minimal server example

import { McpServer, type ToolDefinition, z } from 'zero-mcp';

const server = new McpServer({
  name: 'calculator',
  version: '1.0.0',
});

server.tool({
  name: 'add',
  description: 'Simple addition tool.',
  schema: z.object({
    a: z.number().describe('First addend'),
    b: z.number().describe('Second addend'),
  }),
  handler: async ({ a, b }) => {
    return [
      {
        type: 'text',
        text: `The sum of ${a} and ${b} is ${a + b}.`,
      },
    ];
  },
});

await server.start({
  host: '127.0.0.1',
  port: 3000,
  path: '/mcp',
});

console.log('Ready on http://127.0.0.1:3000/mcp');
// Later: await server.stop();

The server spins up a native HTTP listener and responds to MCP JSON-RPC calls at /mcp.

CORS controls

Zero MCP validates the Origin header and emits CORS headers recommended by the MCP HTTP transport guidance. By default, allowedOrigins is set to '*', which is convenient for local tooling. For production, pass an explicit allow-list:

await server.start({
  allowedOrigins: ['https://my-mcp-console.example'],
});

Hooks for diagnostics and analytics

Instrument behaviour by providing hooks either at construction time or when starting the server:

const server = new McpServer({
  name: 'instrumented',
  version: '1.2.0',
  hooks: {
    onClientConnected(name, version, protocolVersion) {
      console.log(`[connect] ${name}@${version} via ${protocolVersion}`);
    },
    onToolRegistered(toolName) {
      console.log(`[register] ${toolName}`);
    },
    onToolCallStarted(toolName, input) {
      console.log(`[call:start] ${toolName}`, input);
    },
    onToolCallFinished(toolName, input, result, elapsedMs) {
      console.log(`[call:finish] ${toolName} in ${elapsedMs.toFixed(1)}ms`);
    },
    onToolCallError(toolName, input, error) {
      console.error(`[call:error] ${toolName}`, error);
    },
    onToolsListRequested() {
      console.log('[tools] list requested');
    },
    onServerError(error) {
      console.error('[server:error]', error);
    },
  },
});

Example project

A runnable weather server lives in example/. Run it locally with:

npm run example

This builds the library, compiles the example, and starts listening on http://localhost:3005/mcp.

License

MIT © Sergii Vashchyshchuk