Coder Sniffer is a tool to help write code for Drupal or its modules. It can detect and automatically fix coding standard errors.
The project provides a coding standard for PHP_CodeSniffer based on the Drupal Coding Standard.
Those checks apply to all versions of Drupal, so you can use Coder 8.x-2.x to check Drupal 7 code.
This sniffer has been created because of the need to run coding standards checks 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.), or setting up pre-commit hooks on all files being committed.