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

Annotations already declare this is a non-read-only, non-destructive, non-idempotent, closed-world operation, so the safety profile is covered. The description adds genuinely useful behavioral context beyond that: waitlist fallback when the class is full, dependence on the gym's own booking rules, and the fact that no payment is taken here.

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 core action and immediately followed by the waitlist caveat and payment clarification. 'Uses the gym's booking rules' is slightly vague filler but still informative enough to keep.

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?

For a booking mutation with no output schema, the description covers the key outcomes (booking, waitlist, no payment) and the rule source. It omits error/edge cases such as already-booked classes or missing membership, but nothing critical to invoking the tool correctly is absent.

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 the schema already documents gym, date, locale, and class_id with sources (my_gyms, my_schedule). The description adds no parameter-level detail such as format or defaults, so the baseline of 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?

States a specific verb and resource ('Books a class') plus the actor and scope ('signed-in member with their own membership'), which is unambiguous. It does not explicitly distinguish itself from sibling cancel_booking or explain why it is preferred over a waitlist-related tool, so it stops short of 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 rather than spelled out: the reader learns it applies to the signed-in member's own membership and that a waitlist is used when full. There is no explicit when-to-use/when-not-to-use guidance or reference to the sibling tools (cancel_booking, my_bookings) that would route the agent correctly.

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