# Fastapi Expert

Use when building high-performance async Python APIs with FastAPI and Pydantic V2.

- Repository: https://github.com/Jeffallan/claude-skills (12164 stars)
- Category: Data and ML
- License: MIT
- Last updated: 2026-10-30
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add Jeffallan/claude-skills --skill fastapi-expert -g -a claude-code -y`
Codex: `npx skills add Jeffallan/claude-skills --skill fastapi-expert -g -a codex -y`
Cursor: `npx skills add Jeffallan/claude-skills --skill fastapi-expert -g -a cursor -y`
Gemini CLI: `npx skills add Jeffallan/claude-skills --skill fastapi-expert -g -a gemini-cli -y`
Claude Code plugin marketplace: `/plugin marketplace add Jeffallan/claude-skills`

## Description

Use when building high-performance async Python APIs with FastAPI and Pydantic V2. Invoke to create REST endpoints, define Pydantic models, implement authentication flows, set up async SQLAlchemy database operations, add JWT authentication, build WebSocket endpoints, or generate OpenAPI documentation. Trigger terms: FastAPI, Pydantic, async Python, Python API, REST API Python, SQLAlchemy async, JWT authentication, OpenAPI, Swagger Python.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# FastAPI Expert

Deep expertise in async Python, Pydantic V2, and production-grade API development with FastAPI.

## When to Use This Skill

- Building REST APIs with FastAPI
- Implementing Pydantic V2 validation schemas
- Setting up async database operations
- Implementing JWT authentication/authorization
- Creating WebSocket endpoints
- Optimizing API performance

## Core Workflow

1. **Analyze requirements**, Identify endpoints, data models, auth needs
2. **Design schemas**, Create Pydantic V2 models for validation
3. **Implement**, Write async endpoints with proper dependency injection
4. **Secure**, Add authentication, authorization, rate limiting
5. **Test**, Write async tests with pytest and httpx; run `pytest` after each endpoint group and verify OpenAPI docs at `/docs`

> **Checkpoint after each step:** confirm schemas validate correctly, endpoints return expected HTTP status codes, and `/docs` reflects the intended API surface before proceeding.

## Minimal Complete Example

Schema + endpoint + dependency injection in one cohesive unit:

```python
# schemas.py
from pydantic import BaseModel, EmailStr, field_validator, model_config

class UserCreate(BaseModel):
    model_config = model_config(str_strip_whitespace=True)

    email: EmailStr
    password: str
    name: str | None = None

    @field_validator("password")
    @classmethod
    def password_strength(cls, v: str) -> str:
        if len(v) < 8:
            raise ValueError("Password must be at least 8 characters")
        return v

class UserResponse(BaseModel):
    model_config = model_config(from_attributes=True)

    id: int
    email: EmailStr
    name: str | None = None
```

```python
# routers/users.py
from fastapi import APIRouter, Depends, HTTPException, status
from sqlalchemy.ext.asyncio import AsyncSession
from typing import Annotated

from app.database import get_db
from app.schemas import UserCreate, UserResponse
from app import crud

The rest: https://github.com/Jeffallan/claude-skills/blob/HEAD/skills/fastapi-expert/SKILL.md