fastapi_skill

Overview

This skill provides practical guidance and patterns for building secure, high-performance REST APIs and WebSocket services with FastAPI. It focuses on validation, authentication, rate limiting, secure defaults, and async performance patterns to reduce common vulnerabilities and availability risks. The content targets developers who need repeatable, test-driven approaches and deployable best practices.

How this skill works

The skill inspects and prescribes concrete implementation patterns: secure app setup, strict Pydantic validation, JWT/OAuth2 authentication flows, rate limiting, safe file uploads, and async performance techniques like connection pooling and concurrent IO. It includes test-first workflows, CI verification steps, and recommended dependency versions to mitigate known Starlette/FastAPI vulnerabilities. Patterns are actionable, with examples for middleware, dependency injection, caching, pagination, and background tasks.

When to use it

• Building new FastAPI services that require strong security and performance guarantees
• Hardening existing FastAPI apps against DoS, injection, and file upload risks
• Implementing auth (OAuth2/JWT), role-based access, or API key flows
• Designing high-concurrency endpoints that must use async and connection pooling
• Creating predictable, test-driven APIs with CI security checks

Best practices

• Adopt TDD: write failing tests first and implement the minimum to pass
• Validate all inputs with Pydantic models and custom validators
• Use secure defaults: HTTPS, restrictive CORS, and security headers middleware
• Apply rate limiting on auth and public endpoints to mitigate abuse
• Use async connection pools, asyncio.gather for parallel IO, and background tasks for long jobs
• Enforce dependency and framework versions that include CVE fixes

Example use cases

• Secure user registration and login using Pydantic validation and JWT access tokens
• File upload endpoint validating magic bytes, size limits, and storing files outside the webroot
• High-throughput dashboard endpoint that concurrently fetches external services with asyncio.gather
• Rate-limited login and data endpoints using slowapi to protect against credential stuffing
• Paginated list APIs using cursor-based pagination to avoid loading large datasets