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

Goes well beyond the readOnlyHint/openWorldHint annotations by disclosing downstream consequences: Atom provisions an account for the buyer, the domain lands in the buyer's account, and an account-claim email is sent after payment. It also gives two operational constraints the annotations cannot convey — never estimate or recompute the price, and hand the pay_url (which serves a real HTTP 402 challenge) to the pay tool rather than fetching it.

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?

Front-loaded with the core action and the disambiguating sibling reference, and every sentence carries a decision rule or a hazard warning. The first paragraph is dense (scope, sibling, provisioning behavior, preconditions all in one block), which costs a little readability but no sentence is filler.

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?

An output schema exists, so the description need not describe the returned pay_url/price — and it correctly focuses on how to handle them instead. Combined with annotations, 10 documented parameters, and explicit routing against three sibling tools, an agent has everything needed to invoke this correctly.

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 baseline is 3; the description adds genuine meaning beyond the schema by insisting buyer_email must be the real end buyer rather than the agent platform, and by framing the name/phone/address fields as registrant (WHOIS) contact data. It does not add format or validation detail beyond what the per-property descriptions already carry, so it stops short of a 5.

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 ('Get a real, payable Machine Payment Protocol (MPP) URL to purchase an ALREADY-LISTED Atom marketplace domain') and immediately bounds scope ('WITHOUT an Atom OAuth connection'). It also names the sibling it is not (get_domain_register_pay_link_guest for unlisted domains), so an agent can pick correctly from the sibling list without opening schemas.

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 explicit conjunctive preconditions: use ONLY when (a) there is no authenticated Atom connection (otherwise prefer get_domain_purchase_pay_link) and (b) MPP-native payment tools are available. That is when-to-use, when-not-to-use, and the named alternative in one place.

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