Checkstyle is a development tool that helps programmers write Java code that adheres to a set of coding standards. It analyzes Java source files and checks for compliance with specified rules, such as naming conventions, formatting, and code structure. This ensures that the code is consistent and maintainable, making it easier for teams to collaborate. By using Checkstyle, developers can catch potential issues early in the coding process, reducing the likelihood of bugs and improving code quality. It can be integrated into various development environments and build systems, allowing for automated checks during the coding and review phases.