The FastAPI Textbook

This is the FastAPI textbook. Read in order for a full education, or jump to a chapter.

It pairs with the SQLAlchemy 2.0 textbook , the Postgres-focused SQLAlchemy textbook , the Pydantic v2 textbook , and the Alembic textbook .

FastAPI Textbook Ch. 1 — Introduction, Architecture, and the ASGI Foundation

FastAPI architecture: ASGI, Starlette, Pydantic, dependency injection, and the design choices that make it tick.

FastAPI Textbook Ch. 2 — Routing, Path Operations, and the Request Anatomy

Path operations, parameter declaration (path / query / body / header / cookie / form / file), routers, prefixes, dependencies on routers, and request internals.

FastAPI Textbook Ch. 3 — Pydantic Models and Request Validation

Request validation with Pydantic v2: BaseModel, Field, validators, custom types, error responses, nested models, discriminated unions, and the FastAPI integration.

FastAPI Textbook Ch. 4 — Response Models, Serialization, and Output Discipline

Output side of FastAPI: response_model, response shaping, custom encoders, status codes, response classes (JSON, HTML, Streaming, File).

FastAPI Textbook Ch. 5 — Dependency Injection in Depth

Dependency injection in FastAPI: Depends, scopes, sub-deps, class-based deps, lifecycle (startup/shutdown), and the patterns from production.

FastAPI Textbook Ch. 6 — Authentication and Authorization

Auth and authz in FastAPI: passwords, JWT, OAuth2 / OIDC, sessions, passkeys, RBAC, scopes, and security best practices.

FastAPI Textbook Ch. 7 — Async, Concurrency, and the Threadpool

Concurrency in FastAPI: async vs sync handlers, the threadpool, AnyIO, blocking traps, structured concurrency, and how to scale.

FastAPI Textbook Ch. 8 — WebSockets, SSE, and Streaming Responses

Real-time FastAPI: WebSockets, broadcast / pub-sub, SSE for one-way streams, StreamingResponse, NDJSON, and disconnect handling.

FastAPI Textbook Ch. 9 — Background Tasks and Task Queues

Background tasks in FastAPI: BackgroundTasks for fire-and-forget, ARQ / Celery / Dramatiq for reliable jobs, scheduling, and long-running operations.

FastAPI Textbook Ch. 10 — Testing FastAPI: Pytest, AnyIO, and Real DBs

Testing FastAPI: TestClient and AsyncClient, dependency overrides, real DB testing with testcontainers, factory fixtures, and CI integration.