debug:fastapi

Debug FastAPI apps through reproduce, isolate, fix, and prevent phases.

9|1|Updated Jan 12, 2026

Search Tags:#debugging #pydantic #fastapi #middleware #cors #dependency-injection #uvicorn

Ready to run

npx skills add https://github.com/SnakeO/claude-debug-and-refactor-skills-plugin --skill debug-fastapi

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Please help me install this Agent Skill.
Skill: debug:fastapi
Source: https://github.com/SnakeO/claude-debug-and-refactor-skills-plugin/tree/main/plugins/debug-and-refactor/skills/debug-fastapi
Command: npx skills add https://github.com/SnakeO/claude-debug-and-refactor-skills-plugin --skill debug-fastapi

SYSTEM DOCUMENTATION & REQUIREMENTS

What problem does it solve?

This skill helps developers systematically debug FastAPI applications by organizing debugging into four phases, making it easier to reproduce, isolate, fix, and prevent regressions for common FastAPI issues such as async/await problems, Pydantic validation errors, DI failures, CORS, and startup circular imports.

Core Features & Use Cases

Structured debugging process: Reproduce, isolate, fix, and prevent regressions with phase-based workflow.
FastAPI-centric tools: uvicorn logging, OpenAPI docs, and middleware debugging patterns to diagnose issues quickly.
Real-world scenarios: handle 422 errors from Pydantic, dependency injection misconfigurations, CORS errors, database session problems, and circular import startups.
Guided Quick Start: Provides actionable steps and code templates to start debugging rapidly.

Quick Start

Use the skill to troubleshoot a FastAPI app experiencing 422 errors by enabling uvicorn logs, validating OpenAPI, and adding a debug middleware.

Frequently Asked Questions about debug:fastapi

High-intent search queries and answers about installing and using this skill.

FAQPage Schema

How do I fix 422 Pydantic validation errors in FastAPI?▼

Resolve FastAPI 422 errors by validating request data against OpenAPI docs and checking Pydantic model definitions. A structured debugging workflow helps reproduce the error, isolate the failing field, apply the correction, and prevent future regressions.

What is the best way to debug FastAPI dependency injection failures?▼

Debug FastAPI dependency injection failures by enabling uvicorn logs to trace resolution errors. A four-phase debugging approach helps reproduce the issue, isolate the misconfigured dependency, fix the injection scope, and prevent similar regressions.

How do I troubleshoot CORS issues in a FastAPI application?▼

Troubleshoot FastAPI CORS issues by using middleware debugging patterns to inspect headers and origins. Systematically reproduce the cross-origin error, isolate the misconfigured middleware, fix the allowed origins, and prevent regressions.

Why does my FastAPI app crash on startup with circular imports?▼

FastAPI startup circular imports happen when modules reference each other before initialization. Diagnose this by checking uvicorn startup logs, isolating the conflicting import path, restructuring the dependencies, and adding import guards to prevent regressions.

How do I handle async/await problems and database session issues in FastAPI?▼

Handle FastAPI async/await and database session issues by tracing execution with uvicorn logs and debug middleware. The structured workflow ensures you reproduce the concurrency bug, isolate the session handling failure, fix the async block, and prevent deadlocks.