oRPC — Typesafe APIs Made Simple

Project Structure

Organize by domain modules with paired contract + router files:

src/
  index.ts                    # Hono app + handler setup
  middlewares/
    auth-middleware.ts         # Session validation -> injects user
  modules/
    contract.ts               # Root barrel: all contracts
    router.ts                 # Root barrel: all routers
    health/
      health.contract.ts
      health.router.ts
    user/
      user.contract.ts
      user.router.ts

Root barrels compose modules: export default { health, user }.

Contract-First Development

Contracts define API shape. Routers implement them with TypeScript enforcement.

// Contract — define shape
import { oc } from "@orpc/contract";
import { z } from "zod/v4";

const userContract = oc
  .route({ tags: ["user"] })
  .errors({ UNAUTHORIZED: {} });

const searchUser = userContract
  .route({ method: "POST", path: "/user/search" })
  .input(z.object({ query: z.string() }))
  .output(z.array(userSchema));

export default { searchUser };

// Router — implement contract
import { implement } from "@orpc/server";
import contract from "./user.contract";

const router = implement(contract).$context<{ headers: Headers }>();

const searchUser = router.searchUser
  .use(authMiddleware)
  .handler(async ({ input, context }) => { /* ... */ });

export default { searchUser };

Procedures

import { os } from "@orpc/server";

const example = os
  .use(aMiddleware)                         // Middleware
  .input(z.object({ name: z.string() }))   // Validate input
  .output(z.object({ id: z.number() }))    // Validate output (recommended)
  .handler(async ({ input, context }) => {  // Handler
    return { id: 1 };
  });

• .handler is the only required step
• Specifying .output improves TypeScript inference speed
• Create reusable bases: const protectedProcedure = os.$context<Ctx>().use(authMiddleware)

Middleware

Auth middleware injects user into context:

export const authMiddleware = os
  .$context<{ headers: Headers }>()
  .middleware(async ({ context, next }) => {
    const session = await auth.api.getSession({ headers: context.headers });
    if (!session) throw new ORPCError("UNAUTHORIZED");
    return next({ context: { ...context, user: session.user } });
  });

Input-aware middleware for authorization guards:

export const membershipGuard = os
  .$context<{ user: User }>()
  .middleware(async ({ context, next }, input: { uuid: string }) => {
    // Check membership using input.uuid + context.user.id
    if (!member) throw new ORPCError("FORBIDDEN");
    return next();
  });

Stack middleware left-to-right: .use(auth).use(guard).handler(...).

Built-ins: onStart, onSuccess, onError, onFinish, dedupeMiddleware.

Error Handling

// Server — throw errors
throw new ORPCError("NOT_FOUND");
throw new ORPCError("BAD_REQUEST", { message: "Invalid input" });

// Contract-defined typed errors
const contract = oc.errors({
  RATE_LIMITED: { data: z.object({ retryAfter: z.number() }) },
});

// Handler uses typed factory
const proc = implement(contract).handler(async ({ errors }) => {
  throw errors.RATE_LIMITED({ data: { retryAfter: 60 } });
});

// Client — handle errors
const [error, data] = await safe(client.doSomething({ id: "123" }));
if (isDefinedError(error)) { /* typed from contract */ }

Hono Integration

import { OpenAPIHandler } from "@orpc/openapi/fetch";
import { Hono } from "hono";

const handler = new OpenAPIHandler(router, { /* plugins, interceptors */ });

const app = new Hono()
  .basePath("/api")
  .use("/rpc/*", async (c, next) => {
    const { matched, response } = await handler.handle(c.req.raw, {
      prefix: "/api/rpc",
      context: { headers: c.req.raw.headers },
    });
    if (matched) return c.newResponse(response.body, response);
    await next();
  });

TanStack Query

import { createTanstackQueryUtils } from "@orpc/tanstack-query";
const orpc = createTanstackQueryUtils(client);

// Queries
useQuery(orpc.user.search.queryOptions({ input: { query } }));

// Mutations
useMutation(orpc.vehicle.add.mutationOptions());

// Infinite queries
useInfiniteQuery(orpc.feed.list.infiniteOptions({
  input: (pageParam) => ({ cursor: pageParam, limit: 20 }),
  initialPageParam: undefined,
  getNextPageParam: (lastPage) => lastPage.nextCursor,
}));

// Keys for invalidation
orpc.vehicle.key()                           // All vehicle queries
queryClient.invalidateQueries({ queryKey: orpc.vehicle.key() });

Event Iterator (SSE / Streaming)

// Server — async generator
const live = os
  .output(eventIterator(z.object({ message: z.string() })))
  .handler(async function* ({ signal }) {
    for await (const payload of publisher.subscribe("topic", { signal })) {
      yield payload;
    }
  });

// Client — consume
for await (const event of await client.live()) {
  console.log(event.message);
}

Use EventPublisher for typed pub/sub between handlers.

Client Setup

import { RPCLink } from "@orpc/client/fetch";
import { createORPCClient } from "@orpc/client";

const link = new RPCLink({
  url: "http://localhost:3000/api/rpc",
  headers: () => ({ Authorization: `Bearer ${getToken()}` }),
});

export const client = createORPCClient(link);

WebSocket: import { RPCLink } from "@orpc/client/websocket".

Detailed Reference

For comprehensive examples, advanced patterns, and full API coverage see:

• Full Reference — Complete documentation with detailed code examples covering contracts, routers, middleware, server handlers, client setup, TanStack Query, event iterators, plugins, file uploads, WebSocket, AI SDK integration, and metadata.