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

Beyond the annotations (readOnlyHint=false, openWorldHint=true, idempotentHint=false), it discloses that the spot is held 30 minutes, that the Stripe Checkout link is on the gym's own account, and that 'Nothing is charged by this tool' — valuable trust context for a payment flow. It does not address what happens if the hold expires or if the tool is re-called after confirmation.

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 purpose and then the call sequence; every clause carries operational information. The telegraphic colon-chained phrasing ('Then call with confirm: true, first_name and last_name: returns...') is dense and slightly awkward to parse but wastes nothing.

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 9-parameter, non-idempotent purchase tool with no output schema, the description covers the flow, the preconditions, the return shape (summary or checkout link) and the follow-up tool. Remaining gaps — expiry/failure behavior and whether a repeated confirm call double-books — are minor but real for a money-touching operation.

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 already 100%, so the baseline is 3; the description earns above that by explaining cross-parameter dependencies the schema only states piecemeal — confirm requires first_name and last_name, and class_id is optional when buying a pack. It also notes the offer_id default (cheapest single entry), which aids selection.

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 compound verb+resource: 'Buys a trial, a single class or a class pack at a Gymmy gym and books the class in one go.' The purchase+booking combination implicitly separates it from a plain booking sibling, but it never names book_class or start_trial explicitly, so an agent must infer the boundary.

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?

Gives a concrete two-call protocol: first call without confirm returns a summary to confirm with the person, second call with confirm: true commits. It also states the follow-up tool (checkout_status) and the eligibility precondition ('any Gymmy account, no membership needed'). What is missing is explicit routing against alternatives such as book_class or start_trial.

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