Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already establish readOnly/openWorld/non-destructive, so the bar is lower, but the description adds real value: the connected-account prerequisite, the fact that HTML bodies include a `links` field with {text, url} pairs, and an explicit prompt-injection caveat that link targets are sender-supplied data, not instructions. It stops short of covering failure modes such as invalid or inaccessible message IDs.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.