trpc-to-mcp

Turn the tRPC procedures you choose into MCP tools.

• Works with tRPC v11 and @modelcontextprotocol/server v2, the MCP TypeScript SDK
• Serve tools over stdio or HTTP
• Use the tRPC context and middlewares on every tool call
• Transform outputs into text, images, or other MCP content
• Return structured content from procedures with an output schema
• Mount on Next.js and other frameworks with mcp-handler

Install

pnpm add trpc-to-mcp @modelcontextprotocol/server

@trpc/server 11 and @modelcontextprotocol/server 2 are peer dependencies. Install mcp-handler 2 only if you use the mcp-handler adapter. Node.js 20 or later is required.

Usage

1. Add McpMeta to your tRPC instance.

import { initTRPC } from "@trpc/server";
import { type McpMeta } from "trpc-to-mcp";

const t = initTRPC.context().meta().create();

2. Enable mcp on the procedures you want as tools.

import { z } from "zod";

export const appRouter = t.router({
  hello: t.procedure
    .meta({
      mcp: {
        enabled: true,
        description: "Say hello to someone",
        // Optional. Defaults to the procedure path with dots replaced by
        // underscores, e.g. "hello" or "user_byId".
        name: "say_hello",
      },
    })
    .input(z.object({ name: z.string().describe("Who to greet") }))
    .query(({ input }) => `Hello ${input.name}`),
});

Inputs must be object schemas from a validator that implements Standard JSON Schema, such as zod 4.2 or later, ArkType, or Valibot with toStandardJsonSchema(). Chained .input() calls are merged into one tool input schema. Subscriptions can’t be tools.

tRPC validates input on every call, so your zod transforms and refinements run as usual. Errors thrown by a procedure, including TRPCError, come back to the client as a tool result with isError: true.

meta.mcp also takes title and annotations. Queries get readOnlyHint: true unless you set it yourself.

Serve your tools

createMcpServer returns an McpServer with your tools registered. You can register more tools, prompts, and resources on it.

Over stdio:

import { serveStdio } from "@modelcontextprotocol/server/stdio";
import { createMcpServer } from "trpc-to-mcp";

serveStdio(() =>
  createMcpServer({ name: "my-app", version: "1.0.0" }, appRouter, { db }),
);