Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover the safety profile (readOnlyHint=true, destructiveHint=false, openWorldHint=false), so the bar is lower. The description adds real context beyond that: Mirabello is broker of record, brochure/floor plan/due-diligence pack are obtainable only on enquiry, and the data is 'Indicative; verify with Mirabello' — a useful accuracy/trust caveat.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.