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

The description discloses critical behavioral traits beyond the annotations: it provisions an account for the buyer, the domain lands in the buyer's account, an account-claim email is sent after payment, the pay_url serves a real HTTP 402 challenge, and the exact server-computed price must be used without recomputation. These details go well beyond the readOnlyHint and openWorldHint annotations, providing essential context for safe invocation.

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?

The description is longer than typical but every sentence earns its place. It is front-loaded with the main purpose and differentiation, then flows into usage conditions and critical behavioral notes. The structure is logical and avoids redundancy. A slight trim could make it tighter, but it remains efficient given the complexity.

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?

Given the tool's complexity (10 parameters, multiple side effects, and a specific payment flow), the description is comprehensive. It covers when to use, what to supply, how to handle the result, and what to avoid. The output schema exists, so not detailing return values is acceptable. Nothing essential is missing for an agent to call 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?

The schema covers all 10 parameters with descriptions, so the baseline is 3. The description adds semantic emphasis beyond the schema: it stresses that the buyer_email must be the real end buyer, not the agent platform, and that registrant contact details are WHOIS data. It also notes that the pay_url/price must be used exactly as returned, though that's not a parameter. This extra guidance justifies a 4.

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 clearly states the tool's purpose: to get a real, payable MPP URL for registering a fresh domain without an Atom connection. It explicitly differentiates from siblings by naming the alternative for curated marketplace listings (get_domain_purchase_pay_link_guest) and the authenticated version (get_domain_register_pay_link). The verb 'get' and resource 'pay link' are specific, and the scope is unambiguous.

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?

The description provides explicit conditions for use: only when there is no authenticated Atom connection (otherwise prefer get_domain_register_pay_link) and when MPP-native payment tools are available. It also tells the agent to hand the returned pay_url to the MPP agent's pay tool rather than fetching or decoding it. This is a clear when/when-not with named alternatives.

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