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

Annotations already declare readOnly/idempotent/openWorld/non-destructive, so the safety profile is covered; the description adds genuinely non-obvious context — which fields come back, that registrant contacts are privacy-redacted post-GDPR, and that no login is required. The redaction note in particular prevents an agent from misreading an empty contact block as a failed lookup. Missing only rate-limit/quotient behavior.

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?

Four short sentences, each doing distinct work: what it does, what it returns, a caveat about redaction, when to call it, and auth posture. Front-loaded and free of filler.

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?

No output schema exists, so enumerating registrar, dates, nameservers and status codes is exactly the missing information an agent needs to plan around the response. The GDPR caveat closes the one plausible gap for a WHOIS 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?

Single parameter with 100% schema description coverage, so the schema fully carries the semantics; baseline is 4. The description confirms scope ("any domain") but adds no format detail beyond the schema's example.

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+resource ("Look up WHOIS / RDAP registration info") and enumerates the returned fields, making the tool's output recognizable at a glance. The phrase "for any domain" quietly scopes it away from the own-account siblings list_my_domains/get_my_domain_transfers, though no sibling is named explicitly.

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 four concrete triggering questions (who owns it, when it expires, what registrar, whether it's available) that map directly to caller intents. It stops short of pointing at alternatives such as search_domains for bulk availability checks, so routing between the two still requires inference.

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