xsMCP

extra-small MCP SDK for mcp builders hating bloat.

Caution

xsMCP has been sunset

Due to frequent MCP updates and a lack of actual users for xsMCP, we archived xsMCP in July 2025.

If MCP is stable enough and there is user interest, we may restart this project.

About

Why is there this project?

@modelcontextprotocol/sdk is large and has dependencies on libraries like zod, express, etc. that you probably don't even want to use.

Like xsAI, xsMCP does not force you to use a particular server or schema library and is very small.

Roadmap

Our current target is Streamable HTTP Client / Server, Stdio have lower priority.

Compatibility

xsMCP v0.1 is targeted to be compatible with the 2025-03-26 revision and is not backward compatible.

HTTP Server Structure

@xsmcp/server-http is based on Web Standards, not Express.

import { createFetch } from '@xsmcp/server-http'
import { createServer } from '@xsmcp/server-shared'
import { serve } from 'srvx'

import * as tools from '...'

const server = createServer({ ...options })

for (const tool of tools) {
  server.addTool(tool)
}

// (req: Request) => Promise<Response>
const fetch = createFetch(server)

// node.js, deno, bun
serve({ fetch })

// cloudflare workers, pages
export default { fetch }

It can be used as a server on its own or with hono, elysia and itty-router for more features:

import { createFetch } from '@xsmcp/server-http'
import { createServer } from '@xsmcp/server-shared'
import { Elysia } from 'elysia'
import { Hono } from 'hono'
import { AutoRouter } from 'itty-router'

import * as tools from '...'

const server = createServer({ ...options })

for (const tool of tools) {
  server.addTool(tool)
}

const fetch = createFetch(server)

// hono
new Hono()
  .post('/mcp', ({ req }) => fetch(req.raw))

// elysia
new Elysia()
  .post('/mcp', ({ request }) => fetch(request))

// itty-router
AutoRouter()
  .post('/mcp', req => fetch(req))

At the same time, it does not depends on any server framework thus minimizing the size.

For simplicity reasons, this server only returns JSON Response, not SSE.

License

MIT

Third Party Licenses

This project partially copies code from the following projects:

Project	License
modelcontextprotocol/specification	MIT
modelcontextprotocol/servers	MIT
modelcontextprotocol/typescript-sdk	MIT
crouchcd/pkce-challenge	MIT
denoland/std	MIT