FastAPI Debugging Guide

Overview

This skill provides a systematic approach to debugging FastAPI applications. FastAPI is built on Starlette and Pydantic, which means debugging often involves understanding async behavior, request validation, and dependency injection patterns.

When to use this skill:

• 422 Unprocessable Entity errors
• Pydantic ValidationError exceptions
• Async/await related issues
• Dependency injection failures
• CORS errors in browser
• 500 Internal Server Errors
• Database session/connection issues
• Circular import errors on startup

Common Error Patterns

1. Pydantic ValidationError (422 Unprocessable Entity)