Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover read-only, idempotent, non-destructive behavior, and the description adds meaningful constraints: only published posts, full body content, Markdown format, and slug-based lookup. This supplements the annotations with useful behavioral context beyond what structured metadata provides.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.