Static analysis tools can analyze code without executing it to find bugs and issues. The document discusses several static analysis tools for PHP like PHPMD, Phan, PHPCS, PHPLOC, Deptrac. It explains what they do, like PHPLOC gathering complexity metrics and Deptrac checking for violations of defined layer dependencies. In the end, it recommends using static analysis in CI and not trusting results blindly without understanding the underlying errors.