Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnly, idempotent, non-destructive, so the safety profile is covered. The description still adds real behavior: results aggregate across every connected calendar, and the date is interpreted in the owner's timezone with today as the default. It stops short of describing ordering, limits, or what fields come back per event.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences: the first front-loads what the tool returns and its scope, the second disambiguates against three siblings. No repeated annotation content and no filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

A one-parameter read tool with full schema coverage and a complete annotation set needs little more; the description covers scope, timezone, default, and sibling disambiguation. The absence of an output schema is minor for a simple event list.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline would be 3, but the description adds the timezone interpretation of the date ('YYYY-MM-DD in the owner's timezone, default today'), which the schema's parameter text does not state. That is genuine meaning beyond the structured field.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('List the events already booked'), plus scope ('on one date ... across every connected calendar') and an answering use case. It is immediately distinguishable from findCalendarSlots, findAppointments, and calendar_list without opening any schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicitly routes the agent: use findCalendarSlots for free times, findAppointments for appointments SkipCalls booked, and calendar_list for connected calendars. Both the when-to-use and the when-to-use-something-else conditions are named.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.