Compare Flask and FastAPI

Flask is a Python web framework for building web applications. It is based on Werkzeug and Jinja 2. It is a minimalist, 'no batteries included' framework. Yet it can be scaled extensively and support complex applications and use cases by adding required functionality as needed. It follows the philosophy that if something needs to be initialized, it should be initialized by the developer.

Fast API is a high-performance web framework for building web applications with Python 3.6+ based on standard Python type hints. It is designed to be high performance and easy to learn.

Let's see how Flask and FastAPI compare on various factors and features and which to choose when.

Flask

FastAPI

Overall

Type

Type
Python microframework for building web applications.
Type
Minimalistic framework based on starlette and pydantic for building fast web applications using async IO.

Author

Release Date

Release Date
2010
Release Date
2018

License

License
MIT License

Website

Adoption and Ease of Use

Popularity [?]

Popularity [?]
5 Stars
Used by 397,000 projects.
Popularity [?]
New addition to the Python web frameworks family but its popularity is on the rise.

Used by

Used by
Netflix, Zillow, Lyft.
Used by
Uber (internal use,) Explosion AI, Microsoft (internal use)

Jobs [?]

Jobs [?]
4.5 Stars
1067 job openings which list Flask as a requirement.
Jobs [?]
1.5 Stars
100 job openings which list Fast API as a requirement.

Performance [?]

Performance [?]
5 Stars
Because it is minimal and doesn't have a lot of overhead, Flask is very performant. Extensions could impact performance negatively.
Performance [?]
5 Stars
High performance.

Flexibility

Flexibility
5 Stars
Very flexible and doesn't require users to use any particular project or code layout. (A structured approach is still recommended.)
Flexibility
5 Stars
Fast API is flexible to code and doesn't restrict users to a particular project or code layout.

Ease of Learning

Ease of Learning
5 Stars
Flask is simple and its core features are not difficult to learn. There are also plenty of online resources available to aid in learning.
Ease of Learning
4.5 Stars
Easy to learn especially for people who are new to web development. However, it doesn't have a large number of online resources, courses and tutorials.
Database Support

RDBMS Support

RDBMS Support
Through Plugins or Extensions
Through Plugins or Extensions
Flask doesn't come with a built-in ORM framework. Developers can use one of many open source libraries or extensions. Such as Flask-SQLAlchemy, Flask-Pony, etc.
RDBMS Support
Through Plugins or Extensions
Through Plugins or Extensions
FastAPI doesn't come with built in ORM, however is compatible with SQLAlchemy, Pydantic ORM mode.

NoSQL Support

NoSQL Support
NoSQL databases are supported through open source libraries or extensions. To use MongoDB with Flask, Flask-PyMong is a popular choice. CouchDB, Cassandra, and DynamoDB are also supported via libraries.
Verdict Flask is a great choice if you want to develop for a NoSQL database.
NoSQL Support
Fast API supports many NoSQL databases like MongoDb, ElasticSearch, Cassandra, CouchDB and ArangoDB. Read more here.
Web & Core Features

Admin Dashboard

Admin Dashboard
Through Plugins or Extensions
Through Plugins or Extensions
No built-in admin panel, but you can use the Flask-Admin extension. It supports a number of backends like SQLAlchemy, MongoEngine, Peewee etc.
Admin Dashboard
Built-in Support
Built-in
Yes, uses Swagger as an API documentation web user interface.

REST Support

REST Support
Supported via extensions such as Flask-RESTful, Flask-Classful, Flask-RESTPlus.
REST Support
Yes, allows developers to build REST APIs quickly.

Security

Security
Despite being a minimalist Framework, Flask does an excellent job of addressing common security concerns like CSRF, XSS, JSON security and more out of the box. 3rd party extensions like Flask-Security can be used for common security measures. However, it requires that developers evaluate these extensions carefully for security risks and apply timely updates manually when vulnerabilities are discovered.
Security
FastAPI provides several tools for many security schemes in the fastapi.security module. Not enough data.

Templating Library

Templating Library
Flask uses Jinja2 out of the box.
Templating Library
FastAPI supports Jinja2 for templating and also supports aiofiles for serving static files

Web Forms

Web Forms
No built-in support but there is Flask-WTF extention. For SQLAlchemy support, that is, to create forms based on models, there is WTForms-Alchemy
Web Forms
Ships with it's own Forms, with basic features.

Authentication

Authentication
Only provides support for cookie-based sessions but there are extensions available for authentication, authorization and account management.
Authentication
Fast API supports OAuth2, JWT and simple HTTP authentiation.

Testing

Testing
Built-in support using Python's unittest framework.
Testing
Using Starlette and pytest.

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Credits This page was made possible thanks to contributions from Soumyaranjan Acharya who provided data and write up for Fast API.

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