FastAPI
Build
Expose a model or workflow through a typed HTTP API you can test.
All capabilities · Programming foundations
Build and consume REST APIs
Design and ship HTTP APIs (FastAPI/Flask/Express), call third-party APIs, handle auth, errors and rate limits.
Explore 3 tools for this projectMarket relevance
Which roles ask for this — and how often
Share of job postings in India, per role, that name this capability.
What employers mean
You should be able to…
- Design REST endpoints (routes, status codes, pagination) for a resource like documents or chat sessions
- Validate request/response bodies with Pydantic models instead of raw dicts
- Call a third-party API (payment gateway, LLM provider) and handle timeouts, retries and rate limits
- Add authentication (API key or OAuth2/JWT) to protect endpoints
- Auto-generate and read OpenAPI/Swagger docs for an API you built or consumed
- Version an API (v1/v2) without breaking existing clients
- Write integration tests against a running API using a test client
Needs first: Write production-quality Python for AI work
Learn — free, link-checked
The few resources that matter
Read · beginner · 120 min · fastapi.tiangolo.com
FastAPI — User Guide / Tutorial
The official, example-driven walkthrough from hello-world to a typed, validated, auto-documented API — the framework Indian AI job posts name most. — FastAPI (tiangolo)
Watch · beginner · 120 min · youtube.com
Python API Development - Comprehensive Course for Beginners
A full build-along (FastAPI + Postgres) showing how routing, models and a database fit together end to end, not just isolated snippets. — freeCodeCamp.org
Read · intermediate · 35 min · api-security.owasp.org
OWASP API Security Project
API-specific risks (broken object auth, excessive data exposure) that generic web security lists miss — directly relevant to LLM API wrappers. — OWASP
Read · intermediate · 45 min · fastapi.tiangolo.com
FastAPI — Security (OAuth2, JWT)
Shows how to add real OAuth2/JWT auth to an API — the exact gap between a toy endpoint and one that's safe to ship. — FastAPI (tiangolo)
Tools for practice
Choose a tool for the job
Start with one tool for each part of your project. You don’t need to learn them all.
3 tools to explore
Pydantic
Build · Test
Define typed schemas and validate the structured data entering your application.
pytest
Test
Turn expected behaviour and failure cases into repeatable Python tests.
Practice
Hinglish conversation summarizer API with validated payloads and key auth
Build a FastAPI service with three endpoints: submit a Hinglish support thread, fetch its auto-generated English summary and priority, and list threads with pagination. Every payload is modelled and validated with Pydantic, write endpoints sit behind an API key, and the OpenAPI docs carry worked examples. Run it locally with Uvicorn and back it with an httpx integration suite that covers the auth, validation and pagination paths.
Start from
Milestones
- Model request/response schemas in Pydantic and stub the three endpoints · ~3h
- Wire the summarise-and-prioritise call and persist threads with limit/offset paging · ~4.5h
- Add API-key auth on writes and turn validation errors into useful 422 bodies · ~3h
- Write the httpx integration suite over auth, paging and validation · ~3h
- Fill the OpenAPI examples and write the README quickstart · ~1.5h
Done when
- GET /docs renders working OpenAPI documentation with example requests
- POST /tickets rejects malformed payloads with a 422 and a clear error message
- GET /tickets supports limit/offset pagination and returns correct total counts
- Protected endpoints return 401 without a valid API key, verified by an automated test
Prove it
Evidence a recruiter can check
- The rendered `/docs` page with real example request and response bodies on all three endpoints
- An httpx test file asserting 422 on a malformed payload, 401 without a key, and correct total counts across two pages
- A curl transcript in the README taking one Hinglish thread from POST through to its summarised GET
- A note on the one endpoint you redesigned mid-build — what the first shape got wrong, and the commit that changed it
Signal it
Built a FastAPI service that summarises code-mixed Hinglish support threads into English with a priority score — Pydantic-validated payloads, API-key auth on writes, and an httpx suite covering auth, paging and validation.
Interview
Questions you'll get asked
- How would you design an endpoint to upload and process a large PDF asynchronously?
- What's the difference between PUT and PATCH, and when do you use each?
- How do you validate that a request body matches an expected schema in FastAPI?
- How would you handle a third-party API that rate-limits you at 60 requests/minute?
- Walk me through how you'd add pagination to a `/documents` list endpoint with 100k rows.
- How do you version an API without breaking mobile clients still on v1?
- What status code would you return if an LLM call times out, and why?