# RuntimeError: Uvicorn worker failed to start

- **ID:** `python/fastapi-runtimeerror-uvicorn-worker-failed-to-start`
- **Domain:** python
- **Category:** system_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

Uvicorn encountered an error during startup, often due to missing dependencies or incorrect application import.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 3.x | active | — | — |

## Workarounds

1. **Ensure correct module path and app instance.** (95% success)
   ```
   uvicorn myapp:app --reload
   ```
2. **Check that all dependencies are installed.** (90% success)
   ```
   pip install -r requirements.txt
   ```

## Dead Ends

- **Reinstalling uvicorn without checking Python version.** — Uvicorn requires Python 3.7+; older versions may cause startup failure. (60% fail)
- **Using wrong module path in uvicorn command.** — If the module path is incorrect, uvicorn cannot find the application. (80% fail)