# Fastapi Patterns > FastAPI patterns, Pydantic schemas, dependency injection, async correctness, response models, error handling, OpenAPI, and auth. Use whenever the project contains `fastapi` in dependencies, files importing from `fastapi`, `@app.get`/`@router.get` decorators, Pydantic BaseModel subclasses used as request/response types, OR the user asks about FastAPI, Pydantic v2, Depends(), HTTPException, OAuth2PasswordBearer, APIKeyHeader, response_model, even if FastAPI is not mentioned by name. Use when this capability is needed. - Skill: `tomevault-io/fastapi-patterns-3` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/fastapi-patterns-3` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/fastapi-patterns-3/raw - Safety review: pending (external: skill-scanner PASS, skillspector PASS) - 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-patterns-3 --- # FastAPI patterns FastAPI 0.136.1, Pydantic 2.13.3 (baseline at time of writing). Verify current versions at https://pypi.org/project/fastapi/ and https://pypi.org/project/pydantic/. Adapt advice to the versions in the project's `requirements.txt`, `pyproject.toml`, or lockfile. Install: `pip install "fastapi[standard]"` ## When to load this skill - Project has `fastapi` in `requirements.txt`, `pyproject.toml`, or `Pipfile` - Files contain `from fastapi import`, `@app.get`, `@router.get` - Pydantic `BaseModel` used as route input/output type - User asks about FastAPI, Pydantic v2, dependency injection, Depends(), response_model, HTTPException, OAuth2, APIKey ## When not to load this skill - Django or Flask without FastAPI - Pydantic used outside a web framework (standalone validation) - GraphQL with strawberry or ariadne ## Reference files | File | Topics | | ------------------------------------------------------------ | ------------------------------------------------------------------------------------------------------------- | | [pydantic-schemas.md](reference/pydantic-schemas.md) | BaseModel, Field(), field_validator, model_validator, model_config, ConfigDict, separate input/output schemas | | [dependency-injection.md](reference/dependency-injection.md) | Depends(), Annotated pattern, yield dependencies, testing overrides | | [async-correctness.md](reference/async-correctness.md) | async def vs def, threadpool behavior, blocking I/O rules | | [response-models.md](reference/response-models.md) | response_model, response_model_exclude_unset, separate schemas | | [error-handling.md](reference/error-handling.md) | HTTPException, custom exception handlers, status codes | | [openapi.md](reference/openapi.md) | Metadata, tags, disabling docs in production, route decorator params | | [auth.md](reference/auth.md) | OAuth2PasswordBearer, JWT, APIKeyHeader, HTTPBasic, timing attacks | | [anti-patterns.md](reference/anti-patterns.md) | Severity-labeled anti-patterns to flag in review | ## References - https://fastapi.tiangolo.com/ - https://pydantic.dev/docs/validation/latest/ - https://fastapi.tiangolo.com/tutorial/security/ - https://fastapi.tiangolo.com/async/ ## Maintenance FastAPI and Pydantic release independently. Pydantic v2 introduced breaking changes from v1; verify the project's Pydantic version before applying patterns. Check PyPI for current versions. --- > Source: [ku5ic/dotfiles](https://github.com/ku5ic/dotfiles) — distributed by [TomeVault](https://tomevault.io).