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

# SIFR-ASYNC-0006: Synchronous workload annotation applied to async function.

> Synchronous workload annotation applied to async function.

`SIFR-ASYNC-0006` belongs to the **Async effect and awaitability** diagnostic family. It means: synchronous workload annotation applied to async function.

## Why It Happens

Sifr tracks suspension and blocking effects statically. This diagnostic fires when async code either does not really suspend, awaits work that cannot suspend, or calls blocking/CPU-heavy work without an explicit offload boundary.

<Info>
  Use `sifr --explain SIFR-ASYNC-0006` locally to see the renderer's exact message template and any machine-applicable suggestions for the compiler version you are running.
</Info>

## Erroneous Code

```python theme={null}
@blocking_io
async def load() -> str:
    await task.sleep(0.0)
    return "done"
```

## How To Fix It

Apply synchronous workload annotations to synchronous functions, not async functions.

## Fixed Code

```python theme={null}
@blocking_io
def load() -> str:
    return read_text("config.txt")
```

## Details

| Field                  | Value                                                               |
| ---------------------- | ------------------------------------------------------------------- |
| Code                   | `SIFR-ASYNC-0006`                                                   |
| Family                 | `ASYNC`                                                             |
| Severity               | Error                                                               |
| Stability              | stable                                                              |
| Owner                  | `sifr_lowering::lower::typing_and_functions`                        |
| Representative fixture | `crates/sifr/tests/e2e/fail/blocking_io_on_async_def_rejected.sifr` |

See the [Error Codes index](/diagnostics/error-codes) for the complete catalog.