tRPC router pattern for type-safe APIs

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                  import { initTRPC } from '@trpc/server';
import { z } from 'zod';

const t = initTRPC.context<{ userId?: string }>().create();
const authed = t.middleware(({ ctx, next }) => {
  if (!ctx.userId) throw new Error('UNAUTHORIZED');
  return next();
});

export const appRouter = t.router({
  snipCreate: t.procedure
    .use(authed)
    .input(z.object({ title: z.string().min(2) }))
    .mutation(async ({ input, ctx }) => ({ id: 'new', title: input.title, userId: ctx.userId }))
});

export type AppRouter = typeof appRouter;

Maintaining separate REST types and frontend client types can be a lot of overhead in TypeScript-heavy teams. With tRPC, the API types flow directly to the client, which reduces duplication and keeps refactors safe. Runtime validation still matters, so I define input schemas (often with Zod) and enforce auth at the procedure boundary. I also keep routers small and group them by domain. The main gotcha is that tRPC is best for first-party clients; if you’re building a public API, OpenAPI/REST can still be the better fit. For internal apps where frontend and backend evolve together, tRPC can be a big productivity boost without sacrificing correctness.

Mateo Rodriguez

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tRPC router pattern for type-safe APIs

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