What the system does
One or two sentences about the users, workflow or business function.
A useful first message
A little context makes the first reply more useful.
You do not need a formal requirements document. A few concrete facts are enough to begin.
What changed
Describe the failure, deadline, upgrade, ownership gap or feature that created urgency.
Environment
If known: Perl version, hosting model, database, deployment constraints or important dependencies.
Production status
Say whether the system is currently live and whether there is an active incident or hard deadline.