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

# MissingDependency

> An optional extra is not installed (SPEC-v0.2 §1.1, §11).

`ctrlrun.MissingDependency` — class, defined at `src/ctrlrun/errors.py:228`

```python theme={null}
class MissingDependency(CTRLRunError)
    def __init__(module: str, extra: str)
```

An optional extra is not installed (SPEC-v0.2 §1.1, §11).

Never `ImportError` or `ModuleNotFoundError`: an operator reads those as a broken
package rather than as an option they did not select. The message names the module that
is missing and the command that installs it.

## Next

* [Python API index](/reference/api/index).
* [Get started](/get-started/quickstart) · [Why](/why).


## Related topics

- [Errors](/reference/errors.md)
- [Running on Postgres](/postgres.md)
- [Export to OpenTelemetry](/guides/export-to-opentelemetry.md)
- [Install](/get-started/install.md)
- [Claims](/CLAIMS.md)