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

Annotations already cover the safety profile (readOnlyHint=true, destructive=false), yet the description adds substantial context: the URL serves a real HTTP 402 challenge, it must be handed to the agent's pay tool rather than fetched/decoded, the price must never be recomputed, and it documents the recoverable 'registrant_contact_required' error with an exact remediation sequence. That is meaningful behavioral depth beyond structured fields, and it does not contradict any annotation.

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?

It is front-loaded with purpose, then usage, then priority, then return handling, then error recovery — a logical ordering where each block earns its place. It is a little long and the link-cli-availability condition is stated twice (once in the first paragraph, once in PAYMENT PRIORITY), which is mild redundancy but not bloat.

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 payment-flow tool with one parameter and an output schema, the description covers everything an agent needs: eligibility, ordering against alternatives, how to handle the returned pay_url, and a concrete recovery path for the expected contact-required error. No gaps an agent would need to guess at.

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 100% on the single 'domain' parameter, so the baseline is 3, but the description adds real semantics by stressing that the domain must be an already-listed/curated Atom marketplace listing, not an arbitrary domain. That constrains valid input beyond the schema's plain 'the listed domain to purchase' text.

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 opens with a specific verb+resource: 'Get a real, payable Machine Payment Protocol (MPP) URL to purchase an ALREADY-LISTED Atom marketplace domain via Stripe SPT.' It also explicitly distinguishes itself from the nearest siblings (register_domain, get_domain_register_pay_link, get_checkout_link) so an agent can select it without opening any 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?

It gives explicit when-to-use constraints (only when an MPP-native agent like link-cli is present, only for curated Atom listings), an explicit when-not (fresh unlisted domain → get_domain_register_pay_link), and a full priority ladder (register_domain priority 1 → this priority 2 → get_checkout_link priority 3). Nothing is left to inference.

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