@askturret/mcp-adapters-fastify

Register an MCP server as a Fastify plugin. Same runtime and the same two entry points as the Express adapter — what differs is the plugin shape Fastify expects.

Registering it

npm install fastify @askturret/mcp-adapters-fastify

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

const app = Fastify();
await app.register(mcpFromOpenApi('./openapi.yaml'), { prefix: '/mcp' });
await app.listen({ port: 7078 });

Note the prefix: unlike Express, where the mount path is an argument to app.use, a Fastify plugin takes it as a registration option. Forgetting it mounts MCP at the root.

The composable form

fastifyMcp is the explicit counterpart, for when you are supplying sources, an executor or policy yourself:

import { fastifyMcp } from '@askturret/mcp-adapters-fastify';

await app.register(fastifyMcp({ sources: [...] }), { prefix: '/mcp' });

Defaults you are opting into

The one-call form applies the Light preset, identical to the Express adapter's: read-only operations exposed automatically when their schemas validate, mutating operations only when explicitly included, stateless HTTP transport, 1 MiB payload bound, 30-second deadline, and the Explorer mounted only outside production.

Requirements and scope

Fastify is a peer dependency, ^4.0.0 || ^5.0.0 — install it yourself. Node 20+.

CI currently exercises Fastify 5; the 4.x range is declared and expected to work but is not covered by a job, so treat it as best-effort until it is. The compatibility matrix is the authority on that and says so explicitly.

Everything framework-neutral — discovery, compilation, the include filter, the user-context allowlist — lives in @askturret/mcp-core. What remains here is the Fastify-shaped part, and it is deliberately short: none of it is policy.

There is no fromFastify export and there never has been. The entry points are mcpFromOpenApi and fastifyMcp. If you are porting from material that names fromFastify, there is nothing to port to.

Full documentation is in the main README.