# PytestUnknownMarkWarning: Unknown pytest.mark.slow - is this a typo?  You can register custom marks to avoid this warning

- **ID:** `python/pytest-marker-unknown-warning`
- **Domain:** python
- **Category:** config_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

A custom marker is used without being registered in pytest.ini/pyproject.toml; pytest emits a warning, and with `-W error` it becomes a failure.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 7.x | active | — | — |
| 8.x | active | — | — |

## Workarounds

1. **** (98% success)
   ```
   # pyproject.toml
[tool.pytest.ini_options]
markers = [
  "slow: marks tests as slow",
  "integration: requires external services",
]

# then
pytest -m slow
   ```
2. **** (90% success)
   ```
   # pyproject.toml
[tool.pytest.ini_options]
addopts = "--strict-markers"
markers = ["slow: slow tests"]
   ```

## Dead Ends

- **** — Changes test semantics (skips instead of conditionally selecting) and loses filtering capability. (90% fail)
- **** — Hides typos in marker names and prevents `--strict-markers` from catching regressions. (70% fail)
- **** — Suppresses all warnings, including real deprecations and correctness issues. (95% fail)