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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint:false, but the description adds valuable behavioral context beyond that: 'Registrant personal data is usually GDPR-redacted — that is normal, not an error' and 'Data is sourced live from the IANA RDAP bootstrap with an rdap.org fallback'. This clarifies expected outcomes and prevents the agent from misinterpreting redacted data as an error. No contradiction with annotations.

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 efficiently structured and front-loaded with the core purpose, then detailed in a logical order: returns, data source, caveat about GDPR, and usage examples. Every sentence adds value; no filler or repetition.

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 single parameter and absence of an output schema, the description thoroughly explains what to expect for both domain and IP inputs, includes data sourcing details, normalizes the GDPR redaction behavior, and offers usage guidance. It is complete and self-contained for this read-only lookup 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?

Schema description coverage is 100% and the parameter description in the schema already states 'A domain name (example.com) or an IPv4/IPv6 address'. The tool description repeats this almost verbatim ('`query` is a domain name or an IPv4/IPv6 address'), adding no new meaning. Baseline of 3 is appropriate since the schema handles the documentation.

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 it is a 'Read-only WHOIS/RDAP lookup for a domain or IP address', specifies the exact data returned for domains and IPs, and explicitly differentiates from the sibling tool 'lookup_dns' ('for DNS records use lookup_dns instead'). This matches the high standard of a specific verb+resource with sibling differentiation.

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 when-to-use guidance: 'Use to check domain ownership, age, or expiry, vet a suspicious domain, or find an abuse contact'. It also gives a direct alternative: 'for DNS records use lookup_dns instead', satisfying the when-not-to-use requirement clearly.

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