fastapi

A set of Python guidelines for building FastAPI web APIs, including project structure, validation, databases, authentication, and security.

In plain words
What is it for?
Use it when creating or reviewing FastAPI services, request and response models, database code, authentication, documentation, and middleware.
Why use it?
It provides consistent patterns for designing API endpoints and handling data, errors, users, and common security concerns.

Cursor rule

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add rules/patrickjs/awesome-cursorrules/fastapi
Clone the repo
git clone --depth 1 https://github.com/PatrickJS/awesome-cursorrules
Per session 427 This file is loaded in full into every session.
When invoked 427 The same file — it is already loaded in full.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00427 $0.00427
Opus 5 $0.00214 $0.00214
Sonnet 5 $0.00085 $0.00085
Haiku 4.5 $0.00043 $0.00043

Measured 2d ago against content hash 0c94b5295310, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

fastapi scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

Origin

Copies of this mod

6 near-identical copies found in the catalogue:

  • fastapi — 97% identical, 7 lines differ
  • fastapi — 97% identical, 7 lines differ
  • fastapi — 97% identical, 6 lines differ
  • fastapi — 97% identical, 7 lines differ
  • fastapi — 97% identical, 7 lines differ
  • fastapi — 95% identical, 1 lines differ
rules/fastapi.mdc · 87 lines

What it actually says

FastAPI Best Practices

Project Structure

  • Use proper directory structure
  • Implement proper module organization
  • Use proper dependency injection
  • Keep routes organized by domain
  • Implement proper middleware
  • Use proper configuration management

API Design

  • Use proper HTTP methods
  • Implement proper status codes
  • Use proper request/response models
  • Implement proper validation
  • Use proper error handling
  • Document APIs with OpenAPI

Models

  • Use Pydantic models
  • Implement proper validation
  • Use proper type hints
  • Keep models organized
  • Use proper inheritance
  • Implement proper serialization

Database

  • Use proper ORM (SQLAlchemy)
  • Implement proper migrations
  • Use proper connection pooling
  • Implement proper transactions
  • Use proper query optimization
  • Handle database errors properly

Authentication

  • Implement proper JWT authentication
  • Use proper password hashing
  • Implement proper role-based access
  • Use proper session management
  • Implement proper OAuth2
  • Handle authentication errors properly

Security

  • Implement proper CORS
  • Use proper rate limiting
  • Implement proper input validation
  • Use proper security headers
  • Handle security errors properly
  • Implement proper logging

Performance

  • Use proper caching
  • Implement proper async operations
  • Use proper background tasks
  • Implement proper connection pooling
  • Use proper query optimization
  • Monitor performance metrics

Testing

  • Write proper unit tests
  • Implement proper integration tests
  • Use proper test fixtures
  • Implement proper mocking
  • Test error scenarios
  • Use proper test coverage

Deployment

  • Use proper Docker configuration
  • Implement proper CI/CD
  • Use proper environment variables
  • Implement proper logging
  • Use proper monitoring
  • Handle deployment errors properly

Documentation

  • Use proper docstrings
  • Implement proper API documentation
  • Use proper type hints
  • Keep documentation updated
  • Document error scenarios
  • Use proper versioning
Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 87 lines · 0 tokens per session scan A 0c94b5295310

Subscribe to this mod's changes

fastapi is a cursor rule published in the GitHub repository PatrickJS/awesome-cursorrules (40,694 stars, last pushed 3mo ago), licensed CC0-1.0. It adds 427 tokens to every session, about $0.0021 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.