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halyard hăl′yərd noun
A rope used to raise or lower a sail, flag, or yard.
tl;dr - use halyard to track the status of jobs or services or servers
Much like signal flags on the sailing ships of the past, halyard is an application that lets you communicate on the state of anything just by sending very simple bits of data to a central location. That central service can then be queried to get a very direct view of the system in question.
In simplest terms, anything can be watched and verified visually.
The possible states are: OK WARN CRITICAL DEAD EXPIRED