FastAPI best practices and patterns for building modern Python web APIs

FastAPI best practices and patterns for building modern Python web APIs is a skill for Claude Code, Codex from AmariahAK/atlarix-skills. It costs 12 tokens per session (517 once invoked), scanned A, original, Apache-2.0.

A set of guidelines for building web APIs in Python with FastAPI, a framework for receiving HTTP requests and returning data. It covers project structure, routes, validation, database access, authentication, errors, and API documentation.

In plain words
What is it for?
Use it to design FastAPI projects, create request and response models, organize routes, validate data, connect databases, add JWT login, handle failures, and generate OpenAPI documentation.
Why use it?
It provides consistent ways to organize an API and check incoming data, reducing avoidable design and maintenance problems. It also outlines patterns for database connections, security, and error responses.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one.

Good fit Use it to design FastAPI projects, create request and response models, organize routes, validate data, connect databases, add JWT login, handle failures, and generate OpenAPI documentation.

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Install with agentmods
npx agentmods add skills/amariahak/atlarix-skills/acr-fastapi
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.

Any agent
npx skills add AmariahAK/atlarix-skills --skill acr-fastapi
Clone the repo
git clone --depth 1 https://github.com/AmariahAK/atlarix-skills

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for FastAPI best practices and patterns for building modern Python web APIs

README.md
[![agentmods](https://agentmods.dev/badge/skills/amariahak/atlarix-skills/acr-fastapi/github.svg)](https://agentmods.dev/skills/amariahak/atlarix-skills/acr-fastapi)
Your own site
<a href="https://agentmods.dev/skills/amariahak/atlarix-skills/acr-fastapi"><img src="https://agentmods.dev/badge/skills/amariahak/atlarix-skills/acr-fastapi/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for FastAPI best practices and patterns for building modern Python web APIs

Your own site · 80×15
<a href="https://agentmods.dev/skills/amariahak/atlarix-skills/acr-fastapi"><img src="https://agentmods.dev/badge/skills/amariahak/atlarix-skills/acr-fastapi.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 12 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 517 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
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 5.1 $0.00012 $0.00517
Opus 5 $0.00006 $0.00259
Sonnet 5 $0.00002 $0.00103
Haiku 4.5 $0.00001 $0.00052

Measured 12d ago against content hash 896931139354, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-11, from the pricing page.

Security

Grade A, and why

FastAPI best practices and patterns for building modern Python web APIs 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 12d 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.

skills/acr-fastapi/SKILL.md · 99 lines

How it starts

The opening of the file, as written. The whole thing — 99 lines — stays where its author put it; the contents beside it link to each section on GitHub.

FastAPI best practices and patterns for building modern Python web APIs

When to use this skill

FastAPI best practices and patterns for building modern Python web APIs

Source

Synced from https://github.com/PatrickJS/awesome-cursorrules/tree/main/rules/fastapi.mdc.

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

Read the full file on GitHub · 99 lines

Files

What ships with it

1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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. 12d ago First seen · 99 lines · 12 tokens per session scan A 896931139354

Subscribe to this mod's changes

FastAPI best practices and patterns for building modern Python web APIs is a skill published in the GitHub repository AmariahAK/atlarix-skills (2 stars, last pushed 5d ago), licensed Apache-2.0. It adds 12 tokens to every session and 517 once invoked, about $0.0001 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 2026-08-31.

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