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

Annotations already declare readOnlyHint=true and openWorldHint=true, but the description adds real value: 'never books, never exposes anyone's raw calendar (only the shared open slots)' discloses a privacy property the annotations do not, and the note about absolute instants plus viewerTimeZone explains a behavioral quirk of the result. It doesn't discuss rate limits, handle-not-found behavior, or empty-result cases.

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?

Three tight sentences with no filler; the core behavior (intersection of availability) is front-loaded, followed by the safety/privacy note and the time-zone caveat in priority order.

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?

For a read-only query tool with full schema coverage and no output schema, the description covers what is returned (shared free slots for the requested duration), the safety profile, and the time-zone handling. It would be complete if it hinted at result ordering, pagination/limits, or what happens when no common slot exists.

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 description coverage is 100%, so the baseline is 3. The description largely restates what the schema already documents (handles as @handle, viewerTimeZone as the organizer's zone, durationMinutes, from/to as the search window) and adds no syntax or constraint detail beyond it, such as the 8-handle max.

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?

The description states a specific verb and resource ('return the meeting times when ALL of them are free'), and pins down the exact semantics with 'the intersection of their availability.' It also implicitly separates itself from the sibling booking tools by emphasizing that it never books and only computes shared open slots.

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?

'Use it to propose a group time' gives a clear usage context, and the read-only framing signals when this is preferable to the booking siblings. It stops short of naming an explicit alternative (e.g., book_group_meeting once a time is chosen) or stating exclusions, so it is clear but not fully routing.

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