Top 44 FastAPI / Flask Interview Questions & Answers (2026)

01 What is Flask? 02 What is FastAPI? 03 What is the difference between WSGI and ASGI? 04 How do you create a basic Flask application? 05 How do you create a basic FastAPI application? 06 What is Pydantic and how does it work in FastAPI? 07 What are Flask Blueprints? 08 What is FastAPI's dependency injection system? 09 How do you handle path parameters in Flask and FastAPI? 10 What is Flask's application context and request context? 11 What is SQLAlchemy and how is it used in Flask? 12 How does FastAPI handle request validation and error responses? 13 What is Flask's g object? 14 What is CORS and how do you enable it in Flask and FastAPI? 15 What is Flask-Migrate? 16 What are FastAPI response models? 17 What is Flask's before_request and after_request? 18 How do you handle environment configuration in Flask? 19 What is FastAPI's async support? 20 What is Flask's session object? 21 What is Uvicorn and how is it used with FastAPI?

01 How do you implement JWT authentication in FastAPI? 02 How does SQLAlchemy async work with FastAPI? 03 What is Flask's application factory pattern? 04 How do you implement background tasks in FastAPI? 05 What is Pydantic v2 and what changed from v1? 06 How do you implement middleware in FastAPI? 07 What is Alembic and how does it work with FastAPI? 08 How do you write tests for Flask and FastAPI applications? 09 What is rate limiting and how do you implement it in FastAPI? 10 What are FastAPI WebSockets? 11 What is the difference between Flask-RESTful and Flask-RESTX? 12 How do you implement file uploads in FastAPI? 13 What is Flask-Login and how does it work? 14 How do you deploy FastAPI to production?

01 What is FastAPI's OpenAPI specification and how is it customized? 02 How do you implement event-driven patterns in FastAPI with Kafka or Redis? 03 What are advanced Pydantic features for complex validation? 04 How do you implement a multi-tenant API with FastAPI? 05 What is the strangler fig pattern for migrating Flask to FastAPI? 06 How does FastAPI handle streaming responses? 07 What is dependency injection with classes and factories in FastAPI? 08 How does FastAPI integrate with GraphQL? 09 What is the repository pattern and how is it implemented in FastAPI?