Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool has no parameters, no output schema, and a simple UI action, the description is largely complete. However, it could briefly mention that the Streamlabs Desktop app must be running or that the action is idempotent, which would make it more robust. Still, for this complexity level, it suffices.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.