# RuntimeError: The session is unavailable because no secret key was set.

- **ID:** `python/flask-session-cookie-secret-key`
- **Domain:** python
- **Category:** config_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

Flask session requires a secret key for signing; not set in app.config.

## Version Compatibility

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

## Workarounds

1. **** (95% success)
   ```
   app.secret_key = 'your-secret-key' # or app.config['SECRET_KEY'] = os.environ.get('SECRET_KEY')
   ```
2. **** (90% success)
   ```
   Generate secure key: import secrets
app.secret_key = secrets.token_hex(16)
   ```

## Dead Ends

- **** — Empty key is considered unset and raises same error. (95% fail)
- **** — Sessions invalidate on restart; need consistent key. (70% fail)