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

Annotations already declare a safe, idempotent, closed-world read, and the description adds substantial context beyond that: the availability rules applied (hours, breaks, days off, existing bookings, same-day notice), a per-slot price that may differ from list price, and the meaning of an empty result. That is exactly the extra behavioral context the annotations cannot express.

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 sentences, front-loaded with what is listed and under what rules, then the return shape, then the empty-result semantics. Every sentence carries distinct information with no redundancy.

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 return contract itself and does so adequately: it names start_time format and timezone, is_after_hours, and the applicable price, plus what an empty list means. Nothing an agent needs in order to call or interpret this tool is missing.

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% and both parameters are documented there, including that service_id comes from list_services. The description adds context about the operator's local time and the single-service/single-date scoping, but no syntax or format detail beyond the schema, so the 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?

The description names a specific verb and resource ('Lists the open start times') and pins the scope to one service on one date, so the operation is unambiguous. It never names or contrasts a sibling tool (e.g. get_booking_link), which is the only thing keeping it from a 5.

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?

Usage is implied: the mention of the 'operator's booking page' and the empty-list case suggests this is a pre-booking availability probe, but it never states when to use it versus get_booking_link or list_services. There are no explicit preconditions or exclusions.

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