Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the burden, and it does add one important trait: this write goes through policy/approval governance, so an agent can expect gating rather than an immediate effect. However it does not disclose what is mutated, whether it is reversible, what approval flow triggers, or what the result looks like.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.