Psalm is a PHP static analysis tool that helps developers catch errors and improve code quality by analyzing their codebase before running it. It's particularly useful for identifying nullable type issues, which can be problematic if not addressed. By using Psalm, developers can ensure their code is maintainable, efficient, and meets the standards of modern software development. The tool provides a high level of strictness levels, allowing developers to focus on critical problems first and work their way up to more stringent levels. With its ability to infer types for 93.79% of the codebase, Psalm helps developers identify potential issues before they become major problems. By integrating Psalm into a continuous integration system, developers can catch errors early and ensure their code is of high quality.