Flow is
a static type
checker for
JavaScript.

Get Started Install Flow
Current Version: v0.48.0

Code Faster.

Tired of having to run your code to find bugs? Flow identifies problems as you code. Stop wasting your time guessing and checking.

Code Smarter.

It's hard to build smart tools for dynamic languages like JavaScript. Flow understands your code and makes its knowledge available, enabling other smart tools to be built on top of Flow.

Code Confidently.

Making major changes to large codebases can be scary. Flow helps you refactor safely, so you can focus on the changes you want to make, and stop worrying about what you might break.

Code Bigger.

Working in a codebase with lots of developers can make it difficult to keep your master branch working. Flow can help prevent bad rebases. Flow can help protect your carefully designed library from your coworkers. And Flow can help you understand the code you wrote six months ago.

Ready to get going?

Type Inference

Using data flow analysis, Flow infers types and tracks data as it moves through your code. You don't need to fully annotate your code before Flow can start to find bugs.

JavaScript, Your Way

Flow is designed to understand idiomatic JavaScript. It understands common JavaScript patterns and many of the weird things we JavaScript developers love to do.

Realtime Feedback

Flow gives you fast feedback while you code by incrementally rechecking your code as you make changes.

Easy Integration

Flow integrates well with many tools, making it easy to insert into your existing workflow and toolchain.