# Fastapi Development

> Enforces best practices for FastAPI development, ensuring scalable, high-performance, and maintainable APIs. Use when working on server-side Python code involving FastAPI. Use when this capability is needed.

- Skill: `tomevault-io/fastapi-development-2` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add tomevault-io/fastapi-development-2`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/fastapi-development-2/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: tomevault-io (https://skillmd.com/u/tomevault-io)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tomevault-io/fastapi-development-2

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# FastAPI Development Standards

## Key Principles
- **Concise & Technical**: Write accurate, functional code.
- **Functional Style**: Prefer pure functions over classes for routes and logic.
- **RORO Pattern**: "Receive an Object, Return an Object". Use Pydantic models for all inputs and outputs.

## Architecture & Structure
- **File Naming**: Lowercase with underscores (e.g., `routers/user_routes.py`).
- **Exports**: Favor named exports.
- **Organization**: Separate exported routers, sub-routes, utilities, static content, and types (models/schemas).

## Coding Standards
- **Type Hints**: Mandatory for all function signatures.
- **Validation**: Use Pydantic models (v2) instead of raw dictionaries.
- **Conditionals**: Avoid unnecessary curly braces. Use one-line syntax for simple conditionals.
- **Async/Sync**:
  - Use `async def` for I/O-bound operations (DB, external APIs).
  - Use `def` for CPU-bound synchronous tasks.

## Error Handling
- **Early Returns**: Handle errors/edge cases first. Happy path goes last.
- **Guard Clauses**: Validate preconditions early.
- **HTTPExceptions**: Use `HTTPException` for expected errors.
- **No Nested Ifs**: Avoid deep nesting.

## Performance
- **Non-blocking**: Minimize blocking I/O. Use async libraries (asyncpg, aiomysql).
- **Caching**: Implement strategies for frequent data.
- **Lazy Loading**: Use for large datasets.

## Dependencies
- FastAPI
- Pydantic v2
- SQLAlchemy 2.0 (if ORM used)

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<!-- tomevault:4.0:skill_md:2026-04-14 -->