Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden. It discloses that the output includes redemption metrics (vouchers issued, redeemed, last-30-day counts), which informs the agent about the return content. The read-only nature is implied by 'List' but not explicitly stated, and no side effects are mentioned.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.