> ## 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.

# Tracing

> Use automatic Effect spans and custom span names for procedures.

Effect procedures are wrapped in Effect spans automatically.

By default, the span name comes from the procedure path in the router.

```ts title="automatic-spans.ts" theme={null}
export const router = {
  users: {
    // span name: "users.get"
    get: effectProcedure.effect(function* () {
      const usersRepo = yield* UsersRepo;
      return yield* usersRepo.findById("1");
    }),
  },
};
```

## Override the span name

Use `.traced(...)` when a stable custom span name is better than the router path.

```ts title="custom-span.ts" theme={null}
const getUser = effectProcedure
  .input(z.object({ id: z.string() }))
  .traced("users.get_by_id")
  .effect(function* ({ input }) {
    const usersRepo = yield* UsersRepo;
    return yield* usersRepo.findById(input.id);
  });
```

## User spans inside procedure spans

Effect-returning callbacks keep their own spans inside the automatic procedure span. This is useful when you use named `Effect.fn(...)` helpers or `Effect.withSpan(...)` inside handlers, providers, or middleware.

```ts title="named-effect-fn.ts" theme={null}
const getUser = effectProcedure.effect(
  Effect.fn("users.repo.lookup")(function* ({ input }) {
    const usersRepo = yield* UsersRepo;
    return yield* usersRepo.findById(input.id);
  }),
);
```

## Error stack traces

When an Effect procedure fails, `effect-orpc` captures stack information near the procedure definition site so spans point to useful application code.

```txt title="example-stack.txt" theme={null}
UserNotFoundError: User not found
    at <anonymous> (/app/src/router.ts:42:28)
    at users.get (/app/src/router.ts:40:35)
```

<Note>
  This page covers the tracing capability. To wire spans to an OpenTelemetry
  exporter, see [OpenTelemetry guide](/effect-v4/guides/opentelemetry).
</Note>

## Next step

Add HTTP/OpenAPI metadata with [OpenAPI metadata](/effect-v4/capabilities/openapi-metadata).