Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, idempotentHint, and destructiveHint false, so the read-only nature is covered. The description adds useful behavioral context by stating the listing must be owned by the authenticated seller and by imposing the exactly-one-of-productId-or-slug constraint, which is not enforced by the schema's required fields.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.