# ERROR: Could not build wheels for foo, which is required to install pyproject.toml-based projects

- **ID:** `python/pip-build-isolation-missing-build-dependency`
- **Domain:** python
- **Category:** install_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

Build backend requires tools (e.g., Cython, numpy) not declared in build-system.requires, and build isolation hides them.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 3.9 | active | — | — |
| 3.10 | active | — | — |
| 3.11 | active | — | — |

## Workarounds

1. **** (85% success)
   ```
   pip install -U pip setuptools wheel cython numpy
pip install foo
   ```
2. **** (80% success)
   ```
   pip install --only-binary=:all: foo
   ```

## Dead Ends

- **** — Requires all build tools pre-installed globally; often fails with missing headers or wrong versions. (55% fail)
- **** — Transient network issues aside, missing build deps won't resolve by retrying. (90% fail)