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.use(...) accepts native oRPC middleware, Effect generator middleware, and middleware callbacks that return an Effect. Use Effect middleware when the middleware needs Effect services, Effect errors, or Effect control flow.

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Gate middleware

A gate runs checks and lets the pipeline continue automatically.
gate.ts
const authedProcedure = effectProcedure.use(function* () {
  const user = yield* CurrentUser;
  yield* requireActiveUser(user);
});

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Wrap middleware

A wrap calls next(...) explicitly and returns its result.
wrap.ts
const authedProcedure = effectProcedure.use(function* ({ next }) {
  const user = yield* CurrentUser;
  yield* requireActiveUser(user);

  return yield* next({
    context: { userId: user.id },
  });
});

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Transform output

output-transform.ts
const wrapped = effectProcedure.use(function* ({ next }, _input, output) {
  const result = yield* next();
  return yield* output({
    ...result.output,
    wrapped: true,
  });
});

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Effect-returning middleware

Effect-returning middleware can use Effect.fn(...) or return Effect.gen(...) directly.
effect-returning.ts
const authedProcedure = effectProcedure.use(
  Effect.fn("middleware.auth")(function* ({ next }) {
    const user = yield* CurrentUser;
    yield* requireActiveUser(user);

    return yield* next({ context: { userId: user.id } });
  }),
);

const auditedProcedure = effectProcedure.use(({ next }) =>
  Effect.gen(function* () {
    yield* Effect.logDebug("continuing through audit middleware");
    return yield* next();
  }),
);
Guard-only Effect middleware can return void; the pipeline continues automatically.

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Reusable Effect middleware

Use .middleware(...) to define Effect middleware once and pass it to .use(...).
reusable.ts
const requireAdmin = effectProcedure.middleware(function* ({ next }) {
  const user = yield* CurrentUser;
  yield* requireAdminUser(user);
  return yield* next();
});

const adminProcedure = effectProcedure.use(requireAdmin);

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Native oRPC middleware still works

native.ts
const withRequestLabel = effectProcedure.use(({ context, next }) =>
  next({
    context: {
      requestLabel: `${context.role}:${context.requestId}`,
    },
  }),
);

const checked = effectProcedure.use(({ context }) => {
  if (!context.requestId) throw new Error("missing request id");
  // Returning void is a native guard: the pipeline continues automatically.
});
Native middleware can split contiguous Effect runtime boundaries. If you need request-local FiberRef continuity across those boundaries in Node, see Node fiber context bridge.

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Next step

Use contracts with Contract-first APIs.
Last modified on June 15, 2026