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

Annotations already declare readOnlyHint/destructiveHint=false and openWorldHint=false; the description goes well beyond by disclosing what is actually returned (a pay_url serving a real HTTP 402 challenge), that the value must be handed off verbatim and never recomputed, that term_years is server-derived, and a specific recoverable error ('registrant_contact_required') with a retry recipe. Minor gap: it doesn't state whether the generated link expires or is idempotent per domain.

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 key distinction and the tool's identity are front-loaded in the first sentence, and the priority/error guidance follows logically. It is dense with parentheticals and ALL-CAPS emphasis, which costs some readability against what is a fairly complex tool, but nearly every sentence carries distinct operational information.

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-link generator embedded in a multi-step flow with an output schema present, the description covers the return value semantics, the handoff contract, the priority against sibling flows, and the registrant-contact recovery path. An agent has everything needed to call it and act on the result 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?

Only one parameter and schema description coverage is 100%, so the schema already defines `domain`; the description adds little beyond it (it clarifies that term_years is not a caller input, which is useful but concerns a non-existent parameter). Baseline 3 for a fully documented single-parameter tool.

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 payable MPP pay URL to register a fresh domain) and explicitly carves out the sibling it is not for: 'an available domain that is NOT a curated Atom marketplace listing — for that, use get_domain_purchase_pay_link instead'. An agent can distinguish it from the other pay-link siblings 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 explicit when-to-use conditions ('ONLY when an MPP-native agent's tools are available in this session'), an explicit priority ordering against register_domain_spt's in-band flow, and what to do when priority 1 is unavailable. It also names the non-alternative case ('NOT with register_domain_spt's own payment flow') and states there is no checkout-link fallback.

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