h3-mcp

Lightweight Model Context Protocol (MCP) server utilities for h3. Zero MCP SDK dependency. (~16kb gzip, dual-era)

One endpoint serves both protocol eras: the stateless 2026-07-28 revision and the initialize-based revisions (2025-11-25, 2025-06-18, 2025-03-26).

[!WARNING] h3-mcp is still evolving and may introduce breaking changes.

👉 Documentation

Quick Start

npx nypm install h3 h3-mcp

import { H3, serve } from "h3";
import { defineMcpHandler, defineTool } from "h3-mcp";

const app = new H3();

app.all(
  "/mcp",
  defineMcpHandler({
    name: "my-server",
    version: "1.0.0",
    tools: [
      defineTool({
        name: "hello",
        description: "Say hello",
        inputSchema: {
          type: "object",
          properties: { name: { type: "string" } },
          required: ["name"],
        },
        handler: async ({ name }) => ({
          content: [{ type: "text", text: `Hello, ${name}!` }],
        }),
      }),
    ],
  }),
);

serve(app, { port: 3000 });

Development

• Clone this repository
• Install latest LTS version of Node.js
• Enable Corepack using corepack enable
• Install dependencies using pnpm install
• Run interactive tests using pnpm dev
• Run the playground using pnpm play
• Run the official conformance suite using pnpm conformance
• Run the docs site using pnpm install && pnpm dev inside docs/

License

Published under the MIT license.