Zend Optimizer is a software tool, which is required to run files encoded with Zend Guard - a well-known application which is employed to encrypt PHP 4, PHP 5, PHP 7 and PHP 8 files with the purpose to protect them from tampering with the code or reverse engineering. Zend Guard is used by a lot of organizations that make paid script applications, so in case you purchase such an application for your site, you'll probably need Zend Optimizer to be present on the server where you will host it. If you're a programmer, you may also use Zend Guard to shield your code and make sure that your website visitors or clients will be unable to change it in any way. Websites that use Zend Optimizer usually perform better because their PHP code is precompiled, therefore it's already optimized and will be executed a lot faster.