FastAPI | FastAPI vs Flask

What is FastAPI?

FastAPI is a modern, fast, web-based framework for building APIs (Application Programming Interfaces) in Python. It is designed to be easy to use, highly performant, and productive for developers. FastAPI is built on top of Starlette, a high-performance asynchronous web framework, and Pydantic, a powerful data validation and serialization library.

FastAPI leverages modern web development practices, such as asynchronous programming (async/await), type hints, and data validation, to build high-performance APIs.

This allows developers to build efficient and scalable web applications that can handle a large number of concurrent requests, making it suitable for building demanding applications.

What is Flask?

Flask is a simple web framework of Python language that helps to build web applications easily and manageably for small to mid-level projects.

If you want to create a simple web application using HTML, CSS, and JavaScript as frontend and Python as backend, then Flask framework will help you create it quickly. The framework has lots of libraries and functionalities that help to make a perfect dynamic website like routing from one page to another, getting the user form data and storing it in the database, etc.

If you are planning to learn Django, which is a full fledge Python framework, we would recoment you to learn Flask first as it makes your concepts clear. You can learn about Flask at flask tutorial.

FastAPI vs Flask

Flask and FastAPI are both popular web frameworks for building APIs and web applications in Python, but they have some differences in terms of features, performance, and use cases.


FastAPI provides several advanced features that are not available in Flask, such as built-in support for asynchronous programming (async/await), automatic data validation based on type hints, automatic API documentation generation, dependency injection, and OAuth2 authentication support.

Flask, on the other hand, is a more minimalist framework that provides basic routing and request-handling capabilities, and developers need to add third-party libraries for additional features like data validation and authentication.


FastAPI is built on top of Starlette, a high-performance asynchronous web framework, which allows for efficient handling of a large number of concurrent requests.

FastAPI’s use of type hints and Pydantic’s data validation also helps in reducing runtime errors and improving performance. Flask, being a simpler framework, may have slightly better performance in very simple use cases, but FastAPI’s asynchronous capabilities make it more suitable for high-performance applications with heavy workloads.

Developer productivity

FastAPI’s use of type hints, automatic data validation, and API documentation generation based on type hints makes it highly productive for developers. It allows for faster development with fewer bugs and better documentation. Flask, on the other hand, requires additional effort to achieve similar levels of validation and documentation.

Learning curve

Flask is known for its simplicity and ease of learning, making it a good choice for beginners or developers who prefer a minimalist framework. FastAPI, with its advanced features and concepts like asynchronous programming, type hints, and dependency injection, may have a steeper learning curve, especially for developers who are new to these concepts.

Use cases

Flask is often used for small to medium-sized projects or when developers prefer a lightweight framework with flexibility and freedom to choose libraries and tools for different features. FastAPI, with its advanced features, is more suitable for larger projects or applications that require high performance, robust data validation, and extensive API documentation. FastAPI’s asynchronous capabilities also make it ideal for applications with high concurrency requirements.

Ecosystem and community

Flask has a mature and extensive ecosystem of third-party libraries, plugins, and extensions, which provides a wide range of options for developers to choose from. FastAPI’s ecosystem is also growing rapidly, but it may not be as extensive as Flask’s ecosystem due to its relative newness in the Python web framework landscape.

However, FastAPI has a growing community of developers, active support, and contributions, which makes it an increasingly popular choice for modern web development.