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Developer's Guide June 4, 2024

Flask vs FastAPI: Which Python Web Framework Fits Your Project Best?

Writen by Mahipalsinh Rana


To make the right choice of the framework of web development it is possible to state that it plays a crucial role in the success or failure of any project. A few paradigms of Python, known for simple syntax and its strong supportive environment, are available for different development needs. Out of them, Flask vs FastAPI are used for web application development, but FastAPI is the library’s most used.

Flask which is a web application framework that is known for having relatively little complexity while at the same time being highly flexible has been a developer’s favorite for quite some time especially when it comes to machine learning and API development. On the other hand, FastAPI is an application that has recently entered the forums due to its efficiency and its capabilities for unpinned async programming.

In this blog post, the pros and cons of Flask and FastAPI will be discussed, and the way to identify which one will be the best for the upcoming web development project will be described.

What is a Web Development Framework?

Web development framework means a set of rules, practices, and guidelines that lets web developers effectively design and implement applications. Essentially, it consists of a set of pre-existing software modules, libraries, and tools that reduce the overall development effort. According to the above description, developers can emphasize creating distinct functions and characteristics unlike getting lost in the lack of protocols, handling of threads, and other complexities of programming.

Also Read: Most Popular Python Web Frameworks to Use in 2024

Programs such as Django, by the Django Software Foundation, are examples of how these tools enhance the production of complex applications with sustainability in mind. Python specifically needs Django which is a high-level, full-stack framework that enables experienced and novice developers. Moreover, for a scalable application, such as a web application, it is possible to use cloud-based services, for example, AWS Lambda that would require NodeJS as an environment, and thus show that there are several possibilities when it comes to web development frameworks.

What is Flask?

Flask is an API that provides critical features to web applications using Python and is built on WSGI specifications. As a micro-web framework, Flask boasts a remarkably simple design and does not compel the user to rely on any particular libraries or tools. This is a conscious decision, rendering the framework as simple as possible, including only the most basic tools necessary for web developers, like routing and handling of requests while retaining the ability to implement additional components.

Another feature that makes Flask more preferable is the fact that it is easy to use which comes in handy with the newbie developers who want to design simple to complicated web applications. In its basic version, Flask incorporates all the necessary components required for application development, and it is powerful enough to underpin small websites for private individuals as well as giant commercial internet stores. ML often favors TensorFlow for implementation due to its compatibility with Python, Python’s libraries for scientific and data analysis, etc.

Flask is implemented massively in the industry, and several companies such as Netflix, Reddit, and Mozilla use Flask for their websites, thus proving its efficiency and flexibility in terms of operation in a wide range of web application fields.

What is FastAPI?

FastAPI is a contemporary web framework for building APIs with Python 3.6 and later versions. It’s designed to offer high performance, comparable to NodeJS and Go, making it an excellent choice for developers looking to optimize speed and efficiency in their web applications. This modern framework is increasingly popular among top-tier companies like Uber and Netflix for its ability to rapidly develop robust APIs.

One of the defining features of FastAPI is its asynchronous request-handling capability, which allows it to manage multiple requests concurrently. This is achieved through the use of the `async` and `await` syntax in Python, which makes it easy to write non-blocking code. For example, declaring an endpoint in FastAPI could be as simple as `async def my_endpoint():`, indicating that the function can perform other tasks while waiting for I/O operations to complete.

Getting started with FastAPI involves setting up the environment, which typically includes installing FastAPI and Uvicorn, an Asynchronous Server Gateway Interface (ASGI) server, using `pip`. Uvicorn is renowned for its lightning-fast performance and is recommended for production environments.

Overall, FastAPI is not just about high performance; it also emphasizes developer convenience and robustness, offering features such as automatic data validation, annotation-based serialization, and interactive API documentation with Swagger UI. This combination of speed, ease of use, and comprehensive features makes FastAPI a compelling choice for modern web application development.

Features of Flask API

  • Flask is intentionally designed to get started quickly and have a simple implementation
  • It is a tool that gives developers the instruments needed to create a web application very fast and requires no setup to be done to run the application.
  • Flask is lightweight and has a modular design, so many series of extensions are provided for Flask for general requirements like ORM, form validation, upload handling, etc.
  • Flask is equipped with a built-in server and debugger by default, which forms a stepping stone for development just by adding a single line of code.
  • Flask uses Jinja2 as its templating and this is again one of the most powerful and easy to use that exists for being able to dynamically generate HTML content.
  • Prepares the development of RESTful applications, as well as managing URL routes using its incorporated actions.
  • With Flask, it is easy to conduct unit testing on your applications; this is important because it allows the developer to test the functionality of the application before releasing it on the market.
  • Some of the make use of Flask include and it has been employed in the development of all kinds of applications, from small and simple applications like personal projects to complex commercial applications.

Features of FastAPI

  • As its name suggests, FastAPI provides high performance, comparable to Node.js and Go, thanks to Starlette for the web parts and Pydantic for the data parts.
  • Another thing is that FastAPI uses the Starlette framework for its web contexts so it can support asynchronous route handlers, which would be good for asynchronous work and concurrency.
  • Type hints are the core feature of the Python language that has functionality in the line of the editor like auto-completing, for type checking as well help in debugging and even documentation for FastAPI.
  • FastAPI comes with auto-generated documentation for the API based on Swagger UI and ReDoc tools which allows performing test operations within a web browser.
  • Data validation and serialization support provided by Pedantic means that your data always works with the stated schema and if there is any messed up data, it is redirected to the right course.
  • Provides one of the best dependency injection systems that could be rather complex but at the same is the most flexible one allowing the sharing of various parameters and services between your application elements.
  • Native support for security and authentication schemes, especially OAuth2, utilizing Password (and hashing), such as JWT tokens.

Also Learn: Cross-Platform App Development Framework for Your Needs

Pros and Cons of Flask vs FastAPI



  • Flask’s minimalistic and flexible design makes it easy to learn and adapt to various project needs.
  • A large community ensures ample learning resources, plugins, and extensions.
  • The straightforward approach of Flask is ideal for newcomers to web development.
  • Widely adopted in the industry, with proven reliability in production environments.


  • Flask can be slower compared to FastAPI, particularly for handling asynchronous tasks.
  • While Flask can be scaled, it may require additional tools and configurations to manage very large applications efficiently.



  • Asynchronous capabilities allow FastAPI to handle large volumes of requests efficiently.
  • Supports modern Python features including type hints, which improve code quality and speed.
  • Generates documentation automatically, making API testing and debugging easier.
  • Designed with scalability in mind, it is ideal for applications expecting heavy traffic or requiring high responsiveness.


  • The use of advanced Python features and asynchronous programming can be challenging for beginners.
  • Although growing rapidly, FastAPI’s community and ecosystem are not as mature as Flask’s.

Python FastAPI vs Flask

When comparing Python frameworks like FastAPI and Flask, it’s essential to evaluate them across several dimensions to understand which might best suit a particular project. Here’s a detailed comparison based on specific criteria such as HTTP methods, data handling, error management, asynchronous capabilities, performance, documentation, and community support:

HTTP Methods
  • Flask: Supports all common HTTP methods such as GET, POST, PUT, DELETE, and PATCH through decorators that make route handling straightforward.
  • FastAPI: It also supports all standard HTTP methods, leveraging modern Python features like async and await, which can be used directly with the HTTP methods for asynchronous route handling.
Passing Parameters and Data Validation
  • Flask: The parameters can be included in the URL directly or in the body of a request. Validation must be done by hand or with external frameworks that allow it like WTForms or Marshmallow.
  • FastAPI: Utilizes Pydantic for data validation, which is built into the framework. This allows for automatic data validation based on Python-type hints, significantly simplifying the process and reducing boilerplate code.
Displaying Error Messages
  • Flask: For routine error handling, outside of using specific modules and packages that deal with errors, a simple and easy solution is to have custom error handlers that will provide complete information in a format when an error occurs.
  • FastAPI: Gives more desired structure in errors due to Pydantic and Starlette tools. Any failed request returns a JSON object with data and an error explaining what exactly went wrong; these responses can be further personalized in the application.
Asynchronous Tasks
  • Flask: Traditionally synchronous, Flask can support asynchronous tasks through extensions like Flask-AsyncIO. However, it is not natively designed for async programming.
  • FastAPI: Native asynchronous support is one of FastAPI’s core features, allowing developers to use async and await directly, making it highly efficient for IO-bound and high-concurrency applications.
  • Flask: While Flask is incredibly flexible and easy to use, it is not optimized for speed compared to FastAPI, especially in handling large volumes of requests or high concurrency without additional tools.
  • FastAPI: Designed with speed in mind, tests show that FastAPI’s performance is on par with Node.js and Go, thanks to its asynchronous capabilities and efficient request handling.
Documentation Support
  • Flask: The tools Swagger and Flask-RESTPlus can be used to document an API where API documentation is required but Swagger and Flask-RESTPlus take some additional setting to integrate with Flask.
  • FastAPI: Saves time from writing this documentation manually and provides Instant API Documentation through Swagger UI ReDoc integration with Pydantic & Starlette. This documentation may be made ‘live’ with your code changes on a real-time basis.
Community Support
  • Flask:  It’s supported by a large and long-standing community that has tons of resources, tutorials, and even third-party modules. This extensive population is advantageous in a way that one does not have to look very far to find someone who can provide answers to most concerns.
  • FastAPI: However, compared to newer frameworks like FastAPI, it is still catching up on the number of users since the features are relatively modern and the performance is very good. It is quite lively and busy with the addition of new tutorials, guides, and third-party tools being created.

Which Python Web Framework Fits Your Project Best?

Choosing between Flask vs FastAPI largely depends on the specific requirements and scale of your project:

Project Complexity and Scale

  • If you have a small or medium-scale project to implement for the first time, or you are new to web application development, then Flask is recommended. This means that since it is relatively easy to use, you are likely to spend a comparatively shorter time in getting your project off the ground if you are to use quite complicated project management software.
  • Determining where to use FastAPI and where to use Starlette is as follows: The relatively higher latency and limited concurrency capability of Starlette make it a better option for relatively simpler tasks that involve managing only a few requests and do not need tremendous performance. Such a type of support as asynchronous support can also have positive consequences in terms of increasing the speed of the large-scale application while the high performance of the system as well can act as the driving force towards such progress.

Development Experience

  • Developers comfortable with modern Python features, especially type hints and asynchronous programming, may find FastAPI more appealing due to its forward-looking design and emphasis on speed.
  • Those who prefer a more traditional, straightforward approach may opt for Flask due to its ease of use and the robustness of its community and plugins.

Future Growth

  • Consider future needs: if your application might need to scale quickly or handle a lot of asynchronous tasks, starting with FastAPI could save time and effort later on.
  • If the application is expected to remain relatively stable in size and complexity, Flask offers a proven, reliable framework that can efficiently meet such requirements.


It is important to understand that Flask vs FastAPI is two different frameworks for developing pyramid-style applications, each of which has its own advantages that make it permeant for many projects. The lightweight and easy coding are the biggest benefits of Flask and that is why it can be recommended for a simple project. It has a vast and active community with many resources and is also great for introductory projects or small-scale projects.

With this, we see that while Flask is a good option for simpler projects, FastAPI has its advantage for more complex application scenarios and higher performance. It also includes features like asynchronous programming which is useful when handling many requests on the same page and it has the ability to check data and document the API as the application is being developed, hence comes in handy when building fast applications.

Apart from this, FastAPI made the job of developers fast and reduced the chances of errors, which is vital for maintaining and enhancing the application. This might make you want to start a new project that requires supporting a lot of data or users and using the most modern technology, and for that, you should look at FastAPI. But remember: The best framework for the project will be chosen according to the requirements and skills of the employees.

Meet the idealistic leader behind Inexture Solutions – Mahipalsinh Rana! With over 15 years of experience in Enterprise software design and development, Mahipalsinh Rana brings a wealth of technical knowledge and expertise to his role as CTO. He is also a liferay consultant with over a decade of experience in the industry. Apart from all he has technical background spans more than 15 years, making him a go-to authority for all things enterprise software development.

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