Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations only declare readOnly/destructive/openWorld/idempotent hints; the description goes well beyond them by disclosing the unguessable 128-bit token URL, the ~15-minute expiry, that no inline bytes are returned, that each call yields a fresh link (explaining idempotentHint=false), and what contact data the file contains.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.