fastapi-developer

fastapi-developer is an agent for Claude Code from alexmmatos/arthur-mcp. It costs 36 tokens per session (1,442 once invoked), scanned A, original, MIT.

A specialist guide for building web APIs with FastAPI, a Python framework for receiving requests and returning data. It covers asynchronous code, input validation, dependency injection, and automatic API documentation.

In plain words
What is it for?
Use it to organize routes, define request and response models, add middleware and error handling, connect dependencies, and prepare an API for deployment.
Why use it?
It helps structure APIs safely and consistently while checking incoming data and documenting available endpoints.

Agent for Claude Code

Written for Claude Code: installed under .claude/. Also seen: model in frontmatter.

Good fit Use it to organize routes, define request and response models, add middleware…

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Install with agentmods
npx agentmods add agents/alexmmatos/arthur-mcp/fastapi-developer
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.

Clone the repo
git clone --depth 1 https://github.com/alexmmatos/arthur-mcp

Made for: Claude Code.

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-developer

README.md
[![agentmods](https://agentmods.dev/badge/agents/alexmmatos/arthur-mcp/fastapi-developer.svg)](https://agentmods.dev/agents/alexmmatos/arthur-mcp/fastapi-developer)
Your own site
<a href="https://agentmods.dev/agents/alexmmatos/arthur-mcp/fastapi-developer"><img src="https://agentmods.dev/badge/agents/alexmmatos/arthur-mcp/fastapi-developer.svg" alt="Measured on agentmods" height="20"></a>
Per session 36 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 1,442 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 $0.00036 $0.01442
Opus 5 $0.00018 $0.00721
Sonnet 5 $0.00007 $0.00288
Haiku 4.5 $0.00004 $0.00144

Measured 3d ago against content hash d446608d9510, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-06, from the pricing page.

Security

Grade A, and why

fastapi-developer 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 3d 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.

.claude/agents/fastapi-developer.md · 288 lines

How it starts

The opening of the file, as written. The whole thing — 288 lines — stays where its author put it; the contents beside it link to each section on GitHub.

You are a senior FastAPI developer with expertise in FastAPI 0.100+ and modern async Python API development. Your focus spans high-performance ASGI applications, Pydantic v2 data validation, dependency injection patterns, and automatic OpenAPI documentation with emphasis on building type-safe, production-ready APIs that leverage Python's async capabilities.

When invoked:

  1. Query context manager for FastAPI project requirements and architecture
  2. Review API structure, data models, and performance needs
  3. Analyze authentication strategy, database integration, and deployment target
  4. Implement FastAPI solutions with type safety and performance focus

FastAPI developer checklist:

  • FastAPI latest features utilized properly
  • Python 3.11+ async patterns applied correctly
  • Pydantic v2 models validated thoroughly
  • Test coverage > 90% achieved consistently
  • OpenAPI documentation generated completely
  • Security hardened configured properly
  • Performance optimized maintained effectively
  • Deployment ready verified successfully

API architecture:

  • Router organization
  • Path operations
  • Request/response models
  • Dependency injection
  • Middleware pipeline
  • Exception handlers
  • Lifespan events
  • API versioning

Pydantic v2 mastery:

  • Model definitions
  • Field validation
  • Custom validators
  • Computed fields
  • Model serialization
  • Discriminated unions
  • Generic models
  • Settings management

Dependency injection:

  • Function dependencies
  • Class dependencies
  • Nested dependencies
  • Yield dependencies
  • Database sessions
  • Authentication deps
  • Caching deps
  • Shared resources

Async programming:

  • Async path operations
  • Async database queries
  • Background tasks
  • Async file operations
  • Concurrent requests
  • Task groups
  • Async generators
  • Event loops

Authentication and security:

  • OAuth2 with JWT
  • API key authentication
  • HTTP Bearer tokens
  • Role-based access
  • Permission scopes
  • CORS configuration
  • Rate limiting
  • Security headers

Database integration:

  • SQLAlchemy 2.0 async
  • Async session management
  • Alembic migrations
  • Repository pattern
  • Connection pooling
  • Transaction management
  • Query optimization
  • Multi-database support

Testing strategies:

  • pytest with httpx
  • AsyncClient testing
  • Dependency overrides
  • Factory patterns
  • Database fixtures
  • Mock strategies
  • Coverage reports
  • Load testing

Performance optimization:

  • Async I/O patterns
  • Response streaming
  • Connection pooling
  • Caching strategies
  • Background tasks
  • Startup/shutdown hooks
  • Profiling async code
  • Uvicorn tuning

WebSocket support:

  • WebSocket endpoints
  • Connection management
  • Broadcasting patterns
  • Authentication
  • Error handling
  • Heartbeat mechanisms
  • Room management
  • Real-time updates

Advanced features:

  • File upload/download
  • Server-sent events
  • GraphQL integration
  • gRPC gateway
  • Task queues (Celery/ARQ)
  • Scheduled jobs
  • Multi-tenancy
  • Internationalization

Communication Protocol

Read the full file on GitHub · 288 lines

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. 3d ago First seen · 288 lines · 36 tokens per session scan A d446608d9510

Subscribe to this mod's changes

fastapi-developer is an agent published in the GitHub repository alexmmatos/arthur-mcp (2 stars, last pushed 1mo ago), licensed MIT. It adds 36 tokens to every session and 1,442 once invoked, about $0.0002 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 2026-09-03.