On the Web Technologies blog they've posted a guide to some of the top PHP code quality assurance tools to ensure your codebase is kept neat, clear and clean from any unnecessary complexity.

You’ve got the good approach dear reader: code quality tools are essential to write solid and error-free PHP code. It can help your colleagues detect defects in the codebase and teach them some key concepts.

Don’t forget however that the advises and data they can provide won’t be appropriate everywhere. Your experience and your analysis skills are the one you should trust first.

The tutorial starts of with some of the tooling you'll need to get the system up and running: Composer for package management, terminal access for command execution and editor/IDE integrations (optional, obviously). It then lists out each of the tools and includes installation steps and links to more information:

• PHP-CS-Fixer (PHP Coding Standards Fixer)
• PHPCS (PHP CodeSniffer)
• PHPMD (PHP Mess Detector)
• PHPStan (PHP Static Analysis Tool)
• PHPUnit and the CRAP metric

It also includes a few "bonus" tools that might be useful to track other quality aspects of your code including PhpLoc (lines of code), PHPMND for detecting "magic" numbers and churn-php for evaluating complexity of code based on number of commits. there's several more listed in the full post so be sure to check it out and see how you can integrate them into your development process.