# fastapi-code-review

Reviews FastAPI applications for routing patterns, Pydantic schemas, dependency injection, and blocking calls inside async endpoints.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 382 installs · ★ 85
- Author: existential-birds
- License: Apache-2.0 · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/existential-birds/beagle/tree/HEAD/plugins/beagle-python/skills/fastapi-code-review/SKILL.md
- Updated: 2026-09-15
- HTML: https://affpapa.org/en/nevibecode/skills/fastapi-code-review

## What it does

This skill evaluates FastAPI route definitions against standard framework practices. It detects blocking calls such as `requests`, `open()`, and `time.sleep` inside `async def` handlers. It also checks route decorators for explicit status codes, `response_model` declarations, and clean `yield` dependency teardown.

To reduce false positives, the skill enforces three sequential verification gates anchored to exact `file:line` locations before writing a finding. If an issue lacks concrete code evidence, the finding gets downgraded or withdrawn. Valid FastAPI patterns, such as returning a plain dictionary when a `response_model` is defined or using sync dependencies within async endpoints, are explicitly excluded from reporting.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add existential-birds/beagle --skill fastapi-code-review -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/fastapi-code-review/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/fastapi-code-review/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add existential-birds/beagle --skill fastapi-code-review -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/fastapi-code-review/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add existential-birds/beagle --skill fastapi-code-review -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/fastapi-code-review/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install existential-birds/beagle fastapi-code-review
```

2. **Manually: put the files in place**
- File: `.github/skills/fastapi-code-review/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add existential-birds/beagle --skill fastapi-code-review -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/existential-birds/beagle --path plugins/beagle-python/skills/fastapi-code-review
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/fastapi-code-review/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add existential-birds/beagle --skill fastapi-code-review -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/existential-birds/beagle/tree/HEAD/plugins/beagle-python/skills/fastapi-code-review/SKILL.md

## When to use it
- detect blocking I/O calls inside async route handlers
- verify dependency cleanup and proper `Depends()` declarations
- check route decorators for missing `response_model` and status codes
- spot bare `except` blocks in FastAPI endpoints

## Example prompts
- Review `app/api/v1/auth.py` for blocking operations and dependency issues
- Check if my FastAPI route handlers use proper status codes and response models
- Run a review on `routers/billing.py` according to FastAPI best practices

## Source text · SKILL.md · Apache-2.0

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 27a910d0a59dcd6b.

BEGIN THIRD-PARTY FILE 27a910d0a59dcd6b
```text
---
name: fastapi-code-review
description: Reviews FastAPI code for routing patterns, dependency injection, validation, and async handlers. Use when reviewing FastAPI apps, checking APIRouter setup, Depends() usage, or response models.
---

# FastAPI Code Review

## Quick Reference

| Issue Type | Reference |
|------------|-----------|
| APIRouter setup, response_model, status codes | [references/routes.md](references/routes.md) |
| Depends(), yield deps, cleanup, shared deps | [references/dependencies.md](references/dependencies.md) |
| Pydantic models, HTTPException, 422 handling | [references/validation.md](references/validation.md) |
| Async handlers, blocking I/O, background tasks | [references/async.md](references/async.md) |

## Review Checklist

- [ ] APIRouter with proper prefix and tags
- [ ] All routes specify `response_model` for type safety
- [ ] Correct HTTP methods (GET, POST, PUT, DELETE, PATCH)
- [ ] Proper status codes (200, 201, 204, 404, etc.)
- [ ] Dependencies use `Depends()` not manual calls
- [ ] Yield dependencies have proper cleanup
- [ ] Request/Response models use Pydantic
- [ ] HTTPException with status code and detail
- [ ] All route handlers are `async def`
- [ ] No blocking I/O (`requests`, `time.sleep`, `open()`)
- [ ] Background tasks for non-blocking operations
- [ ] No bare `except` in route handlers

## Valid Patterns (Do NOT Flag)

These are idiomatic FastAPI patterns that may appear problematic but are correct:

- **Pydantic validates request body automatically** - No manual validation needed when using typed Pydantic models as parameters
- **Dependency injection for database sessions** - Sessions come from `Depends()`, not passed as function arguments
- **HTTPException for all HTTP errors** - FastAPI handles conversion to proper HTTP responses
- **Async def endpoint without await** - May be using sync dependencies or simple operations; FastAPI handles this
- **Type annotation on Depends()** - This is documentation/IDE support, not a type assertion
- **Query/Path/Body defaults** - FastAPI processes these at runtime, not traditional Python defaults
- **Returning dict from endpoint** - Pydantic converts automatically if `response_model` is set

## Context-Sensitive Rules

Only flag issues when the context warrants it:

- **Flag missing validation** ONLY IF the field isn't already in a Pydantic model with validators
- **Flag missing auth** ONLY IF the endpoint isn't using `Depends()` with an auth dependency
- **Flag missing error handling** ONLY IF HTTPException isn't raised appropriately for error cases
- **Flag sync in async** ONLY IF the operation is actually blocking (file I/O, network calls, CPU-bound), not just non-async

## Gates (FastAPI-specific)
```
END THIRD-PARTY FILE 27a910d0a59dcd6b

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First 2740 of 5946 bytes. © existential-birds · Apache-2.0 · https://github.com/existential-birds/beagle/tree/HEAD/plugins/beagle-python/skills/fastapi-code-review/SKILL.md

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