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# buildkit/ExposeProtoCasing

> Protocol names in `EXPOSE` instructions should be lowercase.

Protocol names in `EXPOSE` instructions should be lowercase.

| Property | Value |
| - | - |
| Severity | Warning |
| Category | Style |
| Default | Enabled |
| Auto-fix | Yes (`--fix`) |

## Description

Protocol names in the `EXPOSE` instruction should be specified in lowercase to
maintain consistency and readability.

## Examples

Bad:

```dockerfile theme={null}
EXPOSE 80/TcP
```

Good:

```dockerfile theme={null}
EXPOSE 80/tcp
```

## Auto-fix

The fix lowercases the protocol in `EXPOSE` port specs.

```dockerfile theme={null}
# Before
EXPOSE 8080/TCP

# After (with --fix)
EXPOSE 8080/tcp
```

## Reference

* [buildkit/ExposeProtoCasing](https://docs.docker.com/reference/build-checks/expose-proto-casing/)


## Related topics

- [BuildKit rules](/rules/buildkit/overview.md)
- [buildkit/ExposeInvalidFormat](/rules/buildkit/ExposeInvalidFormat.md)
- [buildkit/FromAsCasing](/rules/buildkit/FromAsCasing.md)
- [buildkit/ConsistentInstructionCasing](/rules/buildkit/ConsistentInstructionCasing.md)
- [buildkit/StageNameCasing](/rules/buildkit/StageNameCasing.md)


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