# ValueError: Unknown distribution option: 'long_description_content_type'

- **ID:** `python/setuptools-long-description-content-type-error`
- **Domain:** python
- **Category:** config_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

The setup.py uses a keyword argument that is not recognized by the installed version of setuptools (e.g., older setuptools).

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 3.8 | active | — | — |
| 3.9 | active | — | — |

## Workarounds

1. **Upgrade setuptools to a version that supports this option** (95% success)
   ```
   `pip install --upgrade setuptools>=40.0`
   ```
2. **Use pyproject.toml to specify the content type** (90% success)
   ```
   In pyproject.toml: `[project]
...
description = "..."
readme = "README.md"` (which implies content type)
   ```

## Dead Ends

- **Removing long_description_content_type entirely** — This may cause the long description to be rendered as plain text on PyPI, losing formatting. (40% fail)
- **Using a different name like 'content_type'** — The correct parameter name is 'long_description_content_type'; any other name is invalid. (80% fail)