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

Annotations already cover read-only/idempotent/non-destructive, but the description adds real substance beyond them: exact cost ($0.005), payment rail (USDC on Base only), the fact that no check is executed and no payment occurs, pre-payment refusal of other TLDs, absence of contact data in results, and licensing terms on how results may be used.

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 facts (price, no execution, TLD limits) are front-loaded, but the prose is cluttered and repetitive: 'USDC on Base only' appears twice and the .com/.net/.org restriction is restated three times across the response-content and refusal sentences.

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?

With no output schema, the description carries the burden of explaining what the endpoint returns and does so in detail (registrar, dates, status, nameservers, DNSSEC, registry notices, source URL, no contact data). It never describes the structure, fields, or expiry of the quote object this tool itself returns, which is the one remaining gap.

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 has zero parameters, so the baseline is 4. The description still clarifies the only user-supplied value that matters downstream (a single .com/.net/.org domain supplied as ?domain=example.com in the paid GET), which is useful context even though nothing appears in the schema.

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 first clause gives a specific verb+resource ('Returns the payment terms for .../api/domain/whois') plus the price, and immediately scopes what it is not ('this tool never runs the check or pays'). The exact endpoint path also distinguishes it from the similar-sounding sibling domain_precheck_quote, which targets a different resource.

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 tells the agent the tool only yields terms and that the paid call must be made separately ('Pay the 402 over HTTP with x402 v2: GET ?domain=example.com'), and it states hard constraints (one name per call, only .com/.net/.org, other TLDs refused before payment). It stops short of naming the sibling tools (domain_precheck_quote, http/fetch) that carry out the alternatives.

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