> ## Documentation Index
> Fetch the complete documentation index at: https://eo.utopy.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Typed errors

> Create Effect-native errors that map to typed oRPC errors.

`ORPCTaggedError` creates errors that are both:

* yieldable in Effect code
* serializable as oRPC errors

## Define a tagged error

```ts title="errors.ts" theme={null}
import { ORPCTaggedError } from "effect-orpc";
import * as z from "zod";

export class UserNotFoundError extends ORPCTaggedError("UserNotFoundError", {
  code: "NOT_FOUND",
  status: 404,
  message: "User not found",
  schema: z.object({ id: z.string() }),
}) {}
```

## Register it on the builder

```ts title="procedure.ts" theme={null}
const effectProcedure = eos.errors({ UserNotFoundError });
```

## Yield it in a handler

```ts title="get-user.ts" theme={null}
const getUser = effectProcedure
  .input(z.object({ id: z.string() }))
  .effect(function* ({ input }) {
    const user = yield* UsersRepo.findById(input.id);

    if (!user) {
      return yield* new UserNotFoundError({ data: { id: input.id } });
    }

    return user;
  });
```

## Mix regular oRPC errors and tagged errors

```ts title="mixed-errors.ts" theme={null}
const procedure = eos.errors({
  UNAUTHORIZED: { status: 401, message: "Login required" },
  UserNotFoundError,
});

const getUser = procedure.effect(function* ({ errors }) {
  const user = yield* CurrentUser;

  if (!user) {
    return yield* Effect.fail(errors.UNAUTHORIZED());
  }

  return user;
});
```

<Tip>
  Pass tagged error classes to `.errors(...)` so the procedure surface knows
  about the client-visible error type.
</Tip>

## Next step

Add shared behavior with [Middleware](/capabilities/middleware).