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

Annotations cover the safety profile (readOnlyHint, openWorldHint), so the bar is lower, and the description still adds genuine behavior an agent cannot infer: availability is volatile ('times change as other people book'), and returned values are authoritative and must not be normalized. It does not discuss rate limits or result volume.

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, none redundant. The core action is front-loaded, followed by the two operational constraints that actually change agent behavior (no time manipulation, re-fetch when stale).

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, and the description partially compensates by describing the shape of the result (start times grouped by day, in the business's time zone) and naming the starts_at field. For a small read-only lookup with full annotation coverage, that is enough to call the tool correctly; only result paging/volume is unaddressed.

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 all four parameters are already documented, including the days range, from_date format and business slug. The description only indirectly reinforces semantics by mentioning grouping by day and the business time zone. Baseline 3 is appropriate when the schema carries the parameter detail.

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 gives a specific verb and resource ('List the start times a business would offer for one service on its own booking page') plus scope details (grouped by day, business time zone). It clearly describes what comes back, but it does not explicitly contrast itself with the other read siblings like list_my_appointments or get_business.

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 clearly frames the tool as a pre-booking step and constrains downstream use: only these exact times may be booked, and starts_at must be passed to book_appointment unchanged. It also tells the agent to re-run when the user deliberates. It stops short of stating prerequisites explicitly (get_business for service_id is only implied via the schema).

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