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

The annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description still adds real behavior: it performs an availability check ('start is still open'), confirms nothing is booked, and says payment happens externally on Appty. That is genuine context beyond the structured fields, though it doesn't cover failure behavior when a slot is no longer open.

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 the action and its effect, and every sentence earns its place by adding either the availability check, the return value, or the no-booking boundary.

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 present, the description carries the return-value burden and does so ('return a link to the booking page with that service and time selected'). Annotations cover safety and the parameters are fully documented, so nothing an agent needs to call this correctly 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%, so all three parameters (slug, start, service_id) are already documented in the schema, including their provenance (find_open_slots, get_provider). The description adds no syntax or format detail beyond that, 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 states a specific verb and resource: verify a slot is open, then return a booking-page link with the service and time pre-selected. It explicitly carves out the boundary against book_session with 'Nothing is booked here,' so an agent can distinguish the two without opening either 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 clearly frames the use case (produce a link for a client to confirm and pay on Appty) and rules out the booking action, which implicitly routes the agent away from book_session. It never names the alternative tool or states an explicit when-not condition, so it falls short of a 5.

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