NestJS-tRPC

nestjs-trpc lets you define tRPC procedures as decorated NestJS classes instead of chaining t.procedure builders. Routers are DI-aware classes that look like controllers; a separate CLI reads those decorators and emits an AppRouter type for the client.

Verified against v2.13.0. The published docs at nestjs-trpc.io still contain v1-era examples in several places. Where this skill and the docs disagree, this skill matches the shipped .d.ts files and the official examples/ in the repo — see Docs errata for the specific traps.

The one thing to internalize

There are two separate systems that both need to be correct, and they fail independently:

A router that works at runtime but was never picked up by the CLI produces a client with no types, and vice versa. When something is wrong, first ask which of the two is broken.

Setup workflow

1. Install

npm install nestjs-trpc zod @trpc/server

Peer deps (v2.13.0): @nestjs/common & @nestjs/core ^9.3.8 || ^10 || ^11, @trpc/server ^11, zod ^3.14 || ^4, rxjs 7.8.1, reflect-metadata ^0.1.13 || ^0.2. tRPC v11 is required — v10 will not work.

Standard NestJS tsconfig.json requirements apply: experimentalDecorators: true, emitDecoratorMetadata: true. tsc must be resolvable, because the CLI shells out to it to typecheck what it generates.

2. Register the module

// app.module.ts
import { Module } from '@nestjs/common';
import { TRPCModule } from 'nestjs-trpc';
import { UserRouter } from './user.router';
import { UserService } from './user.service';
import { ProtectedMiddleware } from './protected.middleware';
import { AppContext } from './app.context';

@Module({
  imports: [
    TRPCModule.forRoot({
      context: AppContext,
    }),
  ],
  providers: [UserRouter, AppContext, UserService, ProtectedMiddleware],
})
export class AppModule {}

Routers, middlewares, and the context class are all ordinary providers. Listing them in providers is what makes DI work — forgetting a router here is the single most common reason procedures silently don't exist at runtime.

Default mount point is /trpc; override with basePath. Full option table in references/module-config.md.

3. Write a router

// user.router.ts
import { Inject } from '@nestjs/common';
import { Router, Query, Mutation, UseMiddlewares, Input, Ctx } from 'nestjs-trpc';
import { TRPCError } from '@trpc/server';
import { z } from 'zod';
import { UserService } from './user.service';
import { ProtectedMiddleware } from './protected.middleware';
import { userSchema, type User } from './user.schema';

@Router({ alias: 'users' })
export class UserRouter {
  constructor(@Inject(UserService) private readonly userService: UserService) {}

  @Query({
    input: z.object({ userId: z.string() }),
    output: userSchema,
  })
  @UseMiddlewares(ProtectedMiddleware)
  async getUserById(@Input('userId') userId: string): Promise<User> {
    const user = await this.userService.getUser(userId);

    if (user == null) {
      throw new TRPCError({ message: 'Could not find user.', code: 'NOT_FOUND' });
    }

    return user;
  }
}

Client call site: trpc.users.getUserById.query({ userId }). The alias sets that first segment — without it the class name is used.

4. Generate the client type

npx nestjs-trpc generate      # one-shot
npx nestjs-trpc watch         # regenerate on change during development

Writes server.ts (containing export type AppRouter = typeof appRouter) to ./src/@generated by default; --output <dir> moves it. This is a build step, not a runtime import — the generated file is types only, and your procedures still execute through the Nest-managed router at runtime.

Add it to your scripts so it can't drift:

{
  "scripts": {
    "dev": "nestjs-trpc watch & nest start --watch",
    "build": "nestjs-trpc generate && nest build"
  }
}

Run nestjs-trpc generate --dry-run in CI to fail the build when the committed types are stale.

Writing procedures

Three procedure decorators, all taking { input?, output?, meta? }, all optional:

input validates and types the incoming payload. output is optional — omit it and the return type is inferred from the method signature (since v2.11.0). Prefer an explicit output on anything crossing a trust boundary, because it strips fields the client shouldn't see; a leaked password column is the classic version of this bug. Note the example schema above deliberately keeps password in userSchema only to mirror the upstream docs — in real code, define a separate public-facing schema.

Any Standard Schema validator works (Zod, Valibot, ArkType, Yup, Superstruct), but the CLI's schema flattening is built around Zod — stay on Zod unless you have a reason not to.

Parameter decorators pull pieces out of the tRPC opts object:

Throw TRPCError from @trpc/server for client-visible failures. Nest's HttpException is not translated into a tRPC error shape, so it surfaces as an opaque 500.

Details, subscription patterns, and router merging: references/routers.md.

Middlewares and context

Middlewares are @Injectable() classes implementing TRPCMiddleware, applied with @UseMiddlewares(...) on a class (all procedures) or a method (that one only), or globally via globalMiddlewares. Execution order is global → router → procedure → handler.

@Injectable()
export class ProtectedMiddleware implements TRPCMiddleware {
  constructor(@Inject(UserService) private readonly userService: UserService) {}

  async use(opts: MiddlewareOptions<object>): Promise<MiddlewareResponse> {
    const result = await opts.next({ ctx: { user: await this.userService.current() } });
    return result;
  }
}

Two rules that cause most middleware bugs: always return the result of next() so the chain isn't swallowed, and pass added context through next({ ctx }) rather than mutating opts.ctx in place.

Context is a class implementing TRPCContext with a create(opts) method, registered in providers and passed to forRoot({ context }). It runs once per request and is the right home for the request object, session, and per-request loaders.

Full treatment including typing context across a middleware chain and procedure meta: references/middlewares-and-context.md.

Recommended file layout

Mirrors NestJS conventions, which is the whole point of the adapter:

src
├── app.module.ts
├── app.context.ts
├── main.ts
├── @generated/          # CLI output — gitignore or commit, but be consistent
└── user/
    ├── user.router.ts       # the "controller" — thin, no business logic
    ├── user.service.ts      # business logic, unit-testable without tRPC
    ├── user.schema.ts       # Zod schemas + inferred types, shared by both
    └── protected.middleware.ts

Keep routers thin. A router method that only validates, delegates to a service, and maps errors stays testable and keeps the CLI's job easy.

Docs errata

The official docs mix v1 and v2 content. These are the ones that will actually break your build:

• @Ctx(), not @Context(). The routers and middlewares pages show @Context(); the exported decorator is Ctx. (Context as an identifier does exist in the docs' prose as a type name, which is where the confusion comes from.)
• MiddlewareOptions, not TRPCMiddlewareOptions. The latter is not exported.
• TRPCMiddleware<TMeta> — the single generic is the meta type, not the context type. The docs' implements TRPCMiddleware<Context> is wrong. Context types are supplied via MiddlewareOptions<TContext, TReturnContext, TMeta> on the use() signature.
• autoSchemaFile and schemaFileImports are v1 options. They are absent from the v2 TRPCModuleOptions type and will be TypeScript errors, even though the context, client, and integrations pages still show autoSchemaFile. Control output with the CLI's --output flag instead.
• nestjs-trpc/types is a v1 import path. v1's ts-morph generator wrote helper types (Context, {Middleware}Context) into the package; v2's Rust CLI emits a single server.ts instead. Don't import from nestjs-trpc/types on v2 — declare your context types yourself.
• @Middlewares() is deprecated in favour of @UseMiddlewares(), to match @UseGuards.
• The middlewares page's first example has a literal typo (constructror) and a missing async. Don't copy it verbatim.

Reference files

Read these when the task goes past the basics:

• references/routers.md — procedure and parameter decorators in full, subscriptions/SSE with AbortSignal cleanup, alias merging, error handling, testing routers.
• references/middlewares-and-context.md — MiddlewareOptions generics, context propagation and typing, meta-driven authorization, global middleware ordering.
• references/module-config.md — every forRoot option, SSE and JSONL keep-alive settings, onError handlers, custom loggers, transformers.
• references/codegen-and-client.md — CLI flags, ESM --import-extension, schema-flattening failures, consuming AppRouter from React / Next.js / vanilla clients, AppRouterHost for e2e tests and trpc-ui.
• references/api-reference.md — exact exported symbols and type signatures transcribed from the shipped .d.ts. Check here before guessing a name.