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

Annotations already flag this as a non-readonly, open-world, non-idempotent mutation, and the description adds genuinely new behavior: a two-call confirmation gate and that payment happens on the gym's own external Stripe Checkout page. It does not cover failure modes such as an expired or abandoned payment link, or whether membership activates immediately, which keeps it from a 5.

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 the action and payment mechanism, then the call sequence, then the alternative tool. No filler and nothing buried.

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 7-parameter mutation tool with no output schema, the definition covers the full interaction arc: summary, confirmation, payment link, and follow-up status check. Minor gaps remain around what the first call's summary contains and what to do if the person abandons checkout.

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?

With 100% schema description coverage, the schema already explains every parameter, including that confirm is only true after the summary and that first_name/last_name are needed with confirm. The description restates that sequencing and adds provenance for offer_id and gym, but supplies little semantics the schema lacks, 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?

States a specific verb and resource ('Signs the signed-in person up to a Gymmy gym's membership or class pack'), names the source of the offer (get_prices), and names the sibling it is not ('For a single class or a trial with a class, use book_dropin'). An agent can distinguish it from book_dropin and start_trial without opening a 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?

Gives an explicit sequence (first call without confirm returns a summary, then confirm:true with first_name/last_name returns the payment link) and an explicit exclusion routing single classes and trials to book_dropin. It also names checkout_status as the follow-up step, so the agent knows the whole path.

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