We are a group of developers who are passionate about code quality. We have built an innovative lightweight verification tool called the Checker Framework.

The Checker Framework helps you prevent bugs at development time, before they escape to production. It is based on the idea of pluggable type-checking. Pluggable type-checking replaces a programming language's built-in type system with a more powerful, expressive one.

Java's type system prevents some bugs, such as int count = "hello";. However, it does not prevent other bugs, such as null pointer dereferences, concurrency errors, disclosure of private information, incorrect internationalization, out-of-bounds indices, etc.

The Checker Framework enables you to create a more powerful type system and use it in place of Java's. The more powerful type system is not just a bug-finding tool: it is a verification tool that gives a guarantee that no errors (of certain types) exist in your program. Even though it is powerful, it is easy to use. It follows the standard typing rules that programmers already know, and it fits into their workflow. We have created around 20 new type systems, and other people have created many more.

The Checker Framework is popular: it is successfully used on hundreds of projects at Google, Amazon, Uber, on Wall Street, and in other companies from big to small. It it attractive to programmers who care about their craft and the quality of their code. The Checker Framework is the motivation for Java's type annotations feature. Talks on it have received multiple awards at conferences such as JavaOne. With this widespread use, there is a need for people to help with the project: everything from bug fixes, to new features, to case studies, to IDE integration. We welcome your contribution!

Please see our ideas list for how to get started and how to ask questions.