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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so 'Read-only — never modifies data' largely restates structured data. The genuinely additive part is the disclosure of the return shape ('list of free start/end windows'), which matters given there is no output schema, but nothing else (timezone, how existing bookings constrain windows) is disclosed.

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 short sentences, front-loaded with purpose then return shape then use case. Efficient overall, though the trailing read-only sentence is redundant against the annotations and could be dropped without loss.

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?

With no output schema, the description usefully states what comes back, and the required inputs are clear from the schema. Remaining gaps are moderate: timezone/date interpretation and whether omitted calendar scope means 'all calendars' are unspecified for a tool whose whole output depends on scoping.

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 schema already defines date format, the 1–1440 duration range, and activity_calendar_id as an optional UUID filter. The description adds only the loose 'given date and activity duration' framing and never explains what happens when activity_calendar_id is omitted, so baseline 3 applies.

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 ('Find available time slots') and even names the return shape ('list of free start/end windows'). It does not, however, distinguish itself from nearby availability siblings like list_gear_availability or list_room_availability, leaving the agent to infer that this one is the generic/session-oriented variant.

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?

Gives a concrete triggering scenario ('when can we fit a 60-minute session on Friday?'), which is a real when-to-use signal. It stops short of naming alternatives or exclusions, so an agent choosing between this and the gear/room availability tools still has to guess.

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