This plugin allows system administrator to programmatically verify the label assignment correctness on slaves. It is useful to prevent a human error in label assignment when you have a larger number or self-organizing slaves, and generally as a means to make sure your cluster is healthy.
Go to the label configuration page of the label whose assignment you want to validate. For example, http://yourserver/hudson/label/foo/configure.
The script specified here gets executed every time a slave with this label comes online. If the script returns non-zero exit code, the label assignment is considered illegal, and Hudson will mark the slave as offline to prevent it from getting used for a build.
LabelVerifier is an extension point that can be implemented by other plugins, to perform the check in other means.