Code Sniffer is a part of coder (7.x-2.x branch) and a tool to help write code for Drupal or its modules.
The project provides a coding standard for PEAR's PHP_CodeSniffer based on the Drupal Coding Standard.
This sniffer has been created because of the need to run coding standards check without requiring a full drupal installation. This is great for checking code validation on a standalone server without a drupal site, checking a single file from a code editor (Eclipse, Textmate, etc.), setting up pre-commit hooks on all files being committed.