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 tool returns upcoming conferences and includes a default 'days' value, adding behavioral context. However, it does not explain return format, ordering, inclusivity of the start/end dates, or pagination, which is a notable gap for a list operation.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.