Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the behavioral burden; 'Read this' signals a read-only retrieval, and the listed contents (source, computed date, licence, citation) disclose what the agent will get. It does not address output formatting or potential staleness, but that is minor for a zero-parameter metadata tool.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.