fastapi-expert

A development guide for FastAPI, a Python framework for building web APIs. It covers application structure, request validation, asynchronous code, security, testing, documentation, deployment, and performance.

In plain words
What is it for?
Use it to build or review FastAPI endpoints, organize routers and dependencies, validate data with Pydantic, add OAuth2 security, write tests, document APIs, and prepare services for deployment.
Why use it?
It provides practical conventions for designing and maintaining FastAPI services instead of leaving choices about validation, authentication, organization, and testing undefined.

Agent

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 agents/0xfurai/claude-code-subagents/fastapi-expert
Clone the repo
git clone --depth 1 https://github.com/0xfurai/claude-code-subagents
Per session 22 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 436 The whole file, excluding the scripts and references it only reads on demand.
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 $0.00022 $0.00436
Opus 5 $0.00011 $0.00218
Sonnet 5 $0.00004 $0.00087
Haiku 4.5 $0.00002 $0.00044

Measured 2d ago against content hash 462b49e1bb67, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

fastapi-expert 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.

agents/fastapi-expert.md · 57 lines

What it actually says

Focus Areas

  • FastAPI application structure and organization
  • Dependency injection mechanisms in FastAPI
  • Request and response model validation with Pydantic
  • Asynchronous request handling using async/await
  • Security features and OAuth2 integration
  • Interactive API documentation with Swagger and ReDoc
  • Handling CORS in FastAPI applications
  • Test-driven development with FastAPI
  • Deployment strategies for FastAPI applications
  • Performance optimization and monitoring

Approach

  • Organize code with routers and separate modules
  • Leverage Pydantic models for data validation and parsing
  • Utilize dependency injection for scalability and reusability
  • Implement security using FastAPI's OAuth2PasswordBearer
  • Write asynchronous endpoints using async def for performance
  • Enable detailed error handling and custom exception handling
  • Create middleware for logging and request handling
  • Use environmental variables for configuration settings
  • Cache expensive operations with FastAPI's background tasks
  • Optimize startup time and import statements for minimal latency

Quality Checklist

  • Consistent and meaningful endpoint naming
  • Comprehensive openAPI documentation
  • Full test coverage with pytest and fastapi.testclient
  • Statics and media files served efficiently
  • Use of Python type hints throughout the code
  • Validation of all inputs to prevent unsafe operations
  • Secure endpoints with appropriate permissions
  • Positive and negative scenario tests for each endpoint
  • Graceful shutdown implementation with cleanup tasks
  • CI/CD pipeline setup for automated deployment

Output

  • Clear, modular FastAPI code following best practices
  • Robust endpoints with thorough validation and error handling
  • Well-documented API specifications via automatic docs
  • Efficient asynchronous processing with optimal performance
  • Secure and authenticated API with role-based access controls
  • Scalable deployment ready for production environments
  • Comprehensive unit and integration tests ensuring functionality
  • Environmental configuration management for different stages
  • Consistent use of Pydantic for data serialization and validation
  • Performance metrics and logging set up for observability
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 · 57 lines · 22 tokens per session scan A 462b49e1bb67

Subscribe to this mod's changes

fastapi-expert is an agent published in the GitHub repository 0xfurai/claude-code-subagents (994 stars, last pushed 10mo ago), licensed MIT. It adds 22 tokens to every session and 436 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 2026-08-30.