JSpecify

JSpecify is a community-driven effort to standardize null-safety annotations in Java. It provides a formal specification of nullability semantics and a reference set of annotations intended to unify how libraries and tools describe and enforce nullability in APIs and code.

The project aims to address fragmentation caused by a wide variety of existing nullability annotations. It defines core concepts for expressing whether values may be null in parameters, return values, fields, and generic type arguments, as well as policies for default nullability at the package or type level. By establishing a clear, tool-agnostic contract, JSpecify seeks to improve API design, static analysis accuracy, and developer productivity across the Java ecosystem.

JSpecify provides a standardized annotation palette and guidance on their intended meaning and retention. The annotations are designed to be used by library authors and consumer code alike, enabling consistent signals about nullability that can be interpreted by IDEs, compilers, and static analysis tools. The specification emphasizes interoperability across tools and libraries, rather than prescribing a particular runtime behavior.

The project is hosted publicly, with a website at jspecify.org and a presence on code hosting platforms where contributors discuss proposals and publish releases. As an evolving effort, JSpecify remains in active development, growing toward broader adoption as a de facto standard for nullability in Java. It is complementary to tool-specific checkers and frameworks, rather than replacing them.

See also: nullability annotations in Java, Checker Framework, Error Prone, static analysis, API design.