# fastapi.exceptions.RequestValidationError: [{'loc': ['query', 'tags'], 'msg': 'value is not a valid list', 'type': 'type_error.list'}]

- **ID:** `python/fastapi-query-param-list-error`
- **Domain:** python
- **Category:** type_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

A query parameter is declared as List[str] but the client sends a single string without repeated parameters.

## Version Compatibility

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

## Workarounds

1. **** (100% success)
   ```
   Send multiple query parameters: /path?tags=a&tags=b
   ```
2. **** (80% success)
   ```
   Use a string and parse it: tags: str = Query(""), then tags.split(",")
   ```

## Dead Ends

- **** — This is not standard and may break URL encoding. (50% fail)
- **** — The validation still fails because the value is not a list. (70% fail)