Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations provided, the description carries the disclosure burden alone. It usefully enumerates the returned fields (source, date computed, licence, citation), which tells the agent what behavior to expect from this read-only metadata call. It says nothing about permissions, caching, or freshness guarantees, but for a zero-parameter lookup of static metadata the risk surface is minimal, so a 3 is appropriate.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.