> ## 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.

# EffectKeyError

> An effect template cannot be resolved to a key (SPEC-v0.1 §5.1).

`ctrlrun.EffectKeyError` — class, defined at `src/ctrlrun/errors.py:21`

```python theme={null}
class EffectKeyError(CTRLRunError)
```

An effect template cannot be resolved to a key (SPEC-v0.1 §5.1).

The action is refused rather than executed without an effect key: an action whose
logical effect cannot be identified cannot be protected against duplication.

## Next

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


## Related topics

- [Errors](/reference/errors.md)
- [IdentityError](/reference/api/IdentityError.md)
- [Protect a function](/guides/protect-a-function.md)
- [Python API](/reference/api/index.md)
- [DuplicateEffect](/reference/api/DuplicateEffect.md)