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

With no annotations, the description carries the behavioral burden and usefully discloses the per-call cost ($0.001 USDC on Base) and the structured ok/found response shape. It does not mention failure modes, rate limits, or behavior for invalid or unregistered domains, leaving gaps.

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 three dense sentences: it front-loads the purpose and returned fields, then gives the response shape and cost. There is no filler or repetition of schema details.

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 one-parameter lookup with an output schema, the description covers the key operational facts: input, response fields, and cost. The main omissions are error/not-found behavior and caveats about RDAP coverage, but these are minor for this simple tool.

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 already fully documents the single domain parameter with 100% coverage, so the baseline of 3 applies. The description's mention of 'Body {domain}' adds little beyond 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 description clearly identifies a WHOIS lookup via RDAP and enumerates the returned fields (registrar, IANA id, statuses, dates, nameservers, DNSSEC), making the tool's purpose concrete. It does not use an explicit verb like 'retrieves' or differentiate itself from dns_lookup, so it falls just short of a 5.

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 listed fields and 'for any domain' imply the tool is for domain registration metadata rather than DNS resolution, so usage is inferable. However, it never explicitly says when to prefer this over dns_lookup or any alternative.

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