In several places inside Jenkins, a series of "hook scripts" get executed to allow some actions to take place in reaction to some key events. These scripts are written in Groovy, and get executed inside the same JVM as Jenkins, allowing full access to the domain model of Jenkins. For given hook HOOK, the following locations are searched: WEB-INF/HOOK.groovy in jenkins.war WEB-INF/HOOK.groovy.d/*.g