# werkzeug.routing.exceptions.BuildError: Could not build url for endpoint 'static' with values ['filename']. Did you forget to specify values ['filename']?

- **ID:** `python/flask-url-for-external-https`
- **Domain:** python
- **Category:** runtime_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

url_for('static', ...) was called without the required filename argument, or the endpoint name was misspelled.

## Version Compatibility

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

## Workarounds

1. **** (98% success)
   ```
   url_for('static', filename='css/app.css')
   ```
2. **** (85% success)
   ```
   print([r.endpoint for r in app.url_map.iter_rules()])
   ```

## Dead Ends

- **** — Breaks asset links; static files 404 in production. (85% fail)
- **** — Ignores url_prefix and CDN configuration. (70% fail)