@askturret/mcp-adapters-express

Mount an MCP server into an existing Express app. For most people this is the package to install first: one line turns an OpenAPI spec into MCP tools your agents can call.

Five-minute version

npm install express @askturret/mcp-adapters-express

import express from 'express';
import { mcpFromOpenApi } from '@askturret/mcp-adapters-express';

const app = express();
app.use('/mcp', mcpFromOpenApi('./openapi.yaml'));
app.listen(7078);

/mcp now speaks MCP over JSON-RPC 2.0. tools/list returns the operations discovered from your spec; tools/call executes them.

The composable form

When the one-call form stops fitting — several sources, a custom executor, your own policy — expressMcp takes the same runtime with the parts named explicitly:

import { expressMcp } from '@askturret/mcp-adapters-express';

app.use('/mcp', expressMcp({ sources: [...], executor: ... }));

Both forms produce a standard Express Router, so ordinary middleware, mounting and error handling apply.

Defaults you are opting into

The one-call form applies the Light preset, which is chosen to be safe before it is complete:

• read-only operations are exposed automatically, provided their schemas validate;
• mutating operations require explicit inclusion — they do not appear by accident;
• stateless HTTP transport, payloads bounded at 1 MiB, 30-second deadline;
• the local Explorer UI is mounted only when NODE_ENV !== 'production'.

Requirements and scope

Express is a peer dependency, ^4.18.0 || ^5.0.0 — install it yourself, and both majors are exercised by CI. Node 20+.

This package is the Express-shaped part and nothing else. Discovery, compilation, policy and execution all come from @askturret/mcp-core; the same facade backs the Fastify adapter, which is how we know the design is not accidentally Express-shaped. If you are on Fastify, use @askturret/mcp-adapters-fastify — the entry points are identical.

Full documentation and the compatibility matrix are in the main README.