Install Fastify adapter dependencies
To use tRPC with Fastify, install the following dependencies: yarn add @trpc/server fastify zod
server adapters/fastify
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Fastify adapter version requirement
The tRPC v11 Fastify adapter requires Fastify v5 or higher. Using Fastify v4 may cause requests to return empty responses without errors.
Fastify adapter conversion
The tRPC Fastify adapter converts your tRPC router into a Fastify plugin via fastifyTRPCPlugin. When setting up the Fastify server, set the maxParamLength router option to a suitable value to prevent errors during large batch requests.
Fastify HTTP endpoint routes for queries and mutations
After registering the fastifyTRPCPlugin with tRPC, queries are available as GET requests and mutations as POST requests. For example: queries use GET http://localhost:3000/trpc/procedureName?input=INPUT where INPUT is a URI-encoded JSON string, and mutations use POST http://localhost:3000/trpc/procedureName with the request body containing the input data.
Fastify plugin registration example
Example of registering fastifyTRPCPlugin: server.register(fastifyTRPCPlugin, { prefix: '/trpc', trpcOptions: { router: appRouter, createContext, onError({ path, error }) { console.error(`Error in tRPC handler on path '${path}':`, error); }, } satisfies FastifyTRPCPluginOptions<AppRouter>['trpcOptions'], });
Fastify context creation
The context function receives CreateFastifyContextOptions which contains req and res properties. Example: export function createContext({ req, res }: CreateFastifyContextOptions) { const user = { name: req.headers.username ?? 'anonymous' }; return { req, res, user }; }
Fastify plugin options configuration
The fastifyTRPCPlugin accepts the following options: prefix (string, optional, default '/trpc') - URL prefix for tRPC routes; useWSS (boolean, optional, default false) - Enable WebSocket support via @fastify/websocket; trpcOptions (FastifyHandlerOptions<AppRouter, Request, Reply>, required) - tRPC handler options including router, createContext, etc.
Fastify sample router example
Sample Fastify tRPC router with query and mutation: import { initTRPC } from '@trpc/server'; import { z } from 'zod'; type User = { id: string; name: string; bio?: string; }; const users: Record<string, User> = {}; export const t = initTRPC.create(); export const appRouter = t.router({ getUserById: t.procedure.input(z.string()).query((opts) => { return users[opts.input]; }), createUser: t.procedure .input( z.object({ name: z.string().min(3), bio: z.string().max(142).optional(), }), ) .mutation((opts) => { const id = Date.now().toString(); const user: User = { id, ...opts.input }; users[user.id] = user; return user; }), }); export type AppRouter = typeof appRouter;
Fastify server setup example
Example of setting up a Fastify server with tRPC: import { fastifyTRPCPlugin, FastifyTRPCPluginOptions, } from '@trpc/server/adapters/fastify'; import fastify from 'fastify'; import { createContext } from './context'; import { appRouter, type AppRouter } from './router'; const server = fastify({ routerOptions: { maxParamLength: 5000, }, }); server.register(fastifyTRPCPlugin, { prefix: '/trpc', trpcOptions: { router: appRouter, createContext, onError({ path, error }) { console.error(`Error in tRPC handler on path '${path}':`, error); }, } satisfies FastifyTRPCPluginOptions<AppRouter>['trpcOptions'], }); (async () => { try { await server.listen({ port: 3000 }); } catch (err) { server.log.error(err); process.exit(1); } })();
tRPC Fastify adapter
Host tRPC API using Fastify plugin. Refer to adapter-fastify skill for setup and configuration.