@workkit/mcp

Hono for MCP — type-safe Model Context Protocol servers on Cloudflare Workers with REST + OpenAPI from one definition.

Define a tool, resource, or prompt once. Get the MCP JSON-RPC endpoint, a REST surface, an OpenAPI 3.1 spec, and Swagger UI for free. Built on Standard Schema so any validator (Zod, Valibot, ArkType, …) works.

Install

bun add @workkit/mcp @workkit/errors hono zod

Usage

import { createMCPServer } from "@workkit/mcp";
import { z } from "zod";

const server = createMCPServer({
  name: "weather-mcp",
  version: "1.0.0",
  basePath: "/api",
  mcpPath: "/mcp",
  openapi: { enabled: true, swaggerUI: true },
});

server.tool("get-weather", {
  description: "Fetch current weather for a city",
  input: z.object({ city: z.string() }),
  output: z.object({ tempC: z.number(), conditions: z.string() }),
  annotations: { readOnlyHint: true, openWorldHint: true },
  handler: async (ctx) => {
    const data = await fetchWeather(ctx.input.city);
    return { tempC: data.temp, conditions: data.summary };
  },
});

export default server.serve();

Mount on existing Hono app

import { Hono } from "hono";

const app = new Hono();
app.get("/health", (c) => c.text("ok"));
app.route("/", server.toHono());

export default app;

For raw fetch handlers, use server.mount() (no args) — returns { mcpHandler, restHandler, openapi }.

Highlights

• Standard Schema input/output validation — works with Zod, Valibot, ArkType
• Tool annotations follow MCP 2025-06 spec (readOnlyHint, destructiveHint, idempotentHint, openWorldHint)
• One definition → MCP JSON-RPC + REST + OpenAPI 3.1 + Swagger UI
• Hono-style middleware composes per-server, per-tool, or globally
• Pluggable auth: bearer, api-key, or custom middleware
• Optional Durable Object session storage for stateful tools

Documentation

Full guide: workkit docs — MCP Servers