FastAPI Best Practices
Advocacy rules for maintainable, secure, and fast FastAPI services.
How to Use This List
- Review during design reviews and before production deploys.
- Convert repeat failures into automated CI policy where possible.
- Revisit after framework minor upgrades.
Structure
- Keep routers thin and services testable.
- One router module per domain area.
- Colocate Pydantic schemas with routes or a schemas package.
Validation
- Validate at the HTTP boundary with Pydantic 2.
- Use separate input and output models.
- Return 422 bodies compatible with client forms.
Performance
- Use async routes for I/O-heavy handlers.
- Set timeouts on outbound HTTP and DB calls.
- Size DB pools from max connections and worker count.
Security
- Never log tokens or passwords.
- Disable public docs in production when required.
- Apply auth dependencies consistently on protected routers.
FAQs
When should I adopt FastAPI best practices?
Use it when the patterns and trade-offs on this page match your API or data boundary.
What is the top production mistake with FastAPI best practices?
Skipping validation, timeouts, or explicit error contracts at the HTTP edge.
How do I test FastAPI best practices?
Use the framework test client, override dependencies, and assert status plus JSON shape.
Does FastAPI best practices work with Python 3.14?
Yes - examples target Python 3.14 with pinned framework versions from the stack footer.
How does FastAPI best practices relate to Pydantic 2?
Validate and serialize at boundaries; keep services working with typed domain objects.
Sync or async?
Prefer async routes when I/O dominates; keep CPU work small or offload to workers.
Where should business logic live?
Thin handlers; services own rules; repositories own queries.
How do I document APIs?
Publish OpenAPI or schema docs that match response models in code.
How do I handle versioning?
Explicit URL or header versioning with deprecation windows - avoid silent breaks.
What should I read next?
Follow the Related links for the next layer of depth in this section.
How do I stay secure?
Authenticate callers, authorize per resource, rate-limit, and never log secrets.
Performance first step?
Measure DB and upstream latency before swapping frameworks.
Related
- FastAPI Basics - Core routes and models
- Dependency Injection - Per-request providers
- Testing FastAPI - Test client patterns
- Deploying FastAPI - Production serving
Stack versions: This page was written for Python 3.14.0 (stable 3.14, maintenance 3.13), FastAPI 0.115+, Django 5.2, Flask 3.1, Pydantic 2, PyTorch 2.6+, pandas 2.2+, Polars 1.x, ruff 0.9+, and uv 0.6+.