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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, destructiveHint=false, openWorldHint=false), so the bar is lower. The description still adds behavioral value by disclosing the query's temporal semantics — it is a point-in-time slot probe, not a range scan — which affects how the agent interprets the result.

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: purpose and domain first, the key disambiguation second, the lookup prerequisite last. No filler and nothing important buried.

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?

There is no output schema, so the description carries the burden of describing what comes back — it never states whether the result is a boolean, a free slot, or a list of alternatives. The serviceTypeId workflow is covered and annotations handle safety, but the return-value gap leaves the definition merely adequate.

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 only 33%: only startIso is documented in the schema. The description compensates partially by defining serviceTypeId as a list_room_types entry with kind 'service' and pointing to list_room_types to obtain it. restaurantId is left entirely unexplained, so the compensation is incomplete.

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 names a specific verb and resource ('check whether a bookable SERVICE ... has a free slot at a specific start time') and explicitly disambiguates from the sibling check_room_availability by contrasting time-slot vs. date-range semantics. An agent can distinguish this from the room and event availability tools 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?

It gives a clear precondition-workflow ('Use list_room_types first to get the service's id') and an implicit routing cue ('not date-range like rooms'). It stops short of naming the alternative tools or stating when this tool should NOT be used, so it is strong but not fully explicit.

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