Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden of behavioral transparency. It indicates a read-only, informative action through the verbs 'Explain' and 'Returns,' suggesting no side effects or destructive behavior. It does not mention authentication, rate limits, or output format, but for a simple explanation tool with no parameters, this is sufficient. A brief statement that it does not modify any system state would elevate it to 5.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.