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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description still adds real behavioral value beyond them: 'as customers see them' signals that returned slots respect customer-facing booking rules rather than an admin view, and the default-date behavior is not encoded anywhere in the schema. Remaining gaps (timezone, whether slots are live, result granularity) are partly mitigated by the output schema.

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?

A single front-loaded sentence with the verb and scope first and the default behavior parenthetically appended. No filler, nothing redundant with the title.

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?

The output schema and annotations remove the burden of describing return values and safety, and the core query is explained. But for a six-parameter tool, the required 'site' parameter is never mentioned and the party/resource filters — which materially alter availability — are left completely unexplained, leaving the agent to infer their effect.

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 50%: site, party, resource and plugin_id carry no descriptions. The description only speaks to service and date, and never explains that party size or resource (staff/room) meaningfully change which slots are returned — the most important semantic for an availability query. It does not compensate for the gaps the schema leaves.

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 ('Finds the free booking times') scoped to a service and a date, which is far more precise than the title alone. It implicitly distinguishes itself from the mutation siblings (add_booking, edit_booking, cancel_booking) by being the read-side availability lookup, though it never names an alternative explicitly.

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?

The parenthetical '(default: the first with any)' explains what happens when date is omitted, which is useful usage guidance. However, there is no statement of when to prefer this tool over a direct booking attempt, no prerequisite context (e.g. check availability before calling add_booking), and no guidance on when to pass party or resource filters.

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