> ## Documentation Index > Fetch the complete documentation index at: https://docs.coderabbit.ai/llms.txt > Use this file to discover all available pages before exploring further. # PHPCS > CodeRabbit's guide to PHPCS. [PHPCS](https://github.com/squizlabs/PHP_CodeSniffer) (PHP CodeSniffer) is a development tool that ensures your code conforms to a coding standard. It is an essential tool for any development team that wants to ensure their code is consistent and follows best practices. ## Files PHPCS will run on files with the following extensions: * `.php` ## Features PHPCS can detect and fix various coding standard violations including: * **PSR Standards**: Enforces PSR-1, PSR-2, PSR-12, and other coding standards * **Custom Standards**: Supports custom coding standards and rules * **Auto-fixing**: Can automatically fix many coding standard violations * **Custom Rules**: Allows creation of custom sniff rules * **Multiple Standards**: Can enforce multiple coding standards simultaneously ## Popular Standards PHPCS supports many coding standards including: * **PSR-1**: Basic Coding Standard * **PSR-2**: Coding Style Guide * **PSR-12**: Extended Coding Style * **Squiz**: Squiz Labs coding standard * **PEAR**: PEAR coding standard * **Zend**: Zend Framework coding standard ## Configuration PHPCS requires a configuration file to run. CodeRabbit will only run PHPCS if one of the following configuration files is found: * `phpcs.xml` - XML configuration file * `phpcs.xml.dist` - Distributed XML configuration file CodeRabbit will not run PHPCS if no configuration file is found. ## When we skip PHPCS CodeRabbit will skip running PHPCS when: * PHPCS is disabled in the review profile (only runs in **Assertive** mode). * No config file is found (`phpcs.xml` or `phpcs.xml.dist`). * The config file does not appear to be a valid PHPCS ruleset (missing `