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

Annotations already declare readOnly, openWorld, idempotent and non-destructive, so the safety bar is low, yet the description still adds substantial behavior: it names the upstream API, the auth mechanism (WHOISFREAKS_API_KEY or per-request key), that calls consume account credits, and that nothing is created or changed. It also discloses the fallback ladder with concrete HTTP signals (206 partial when the registrar doesn't answer, 210 latest stored record) and enumerates the failure outcomes (401/403/404/429) that come back as a short message instead of data.

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?

Structure is strong and front-loaded: purpose first, then routing rules, then input constraint, then return shape and failure codes. The routing sentence and the failure-code parenthetical are dense but each carries real decision value; the description is long mainly because it does a lot of work, though the status-code enumeration could be tightened.

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 does the return-value job itself: fields returned, redaction caveat on contacts, raw WHOIS text, and the two degraded-record states. Auth, cost, failure modes and input form are all covered, leaving nothing an agent needs before calling it.

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 coverage is 100%, so the baseline is 3, but the description does not add meaning for either parameter: the `format` enum (json/xml) is never mentioned. Worse, it instructs "Pass a bare domain (example.com), not a URL" while the schema's domainName description explicitly accepts https://example.com and http://example.com, which is a direct conflict that could make an agent reject a valid input.

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?

Opens with a specific verb and resource ("Get the current WHOIS registration record for a domain") and immediately scopes it as a live query, then enumerates what the record contains. It explicitly distinguishes itself from whoisHistory, bulkWhoisLookup, reverseWhoisLookup and domainAvailability, so an agent can pick it out of a 20+ sibling catalog without opening any 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?

Each alternative is paired with the condition that selects it: past owners and changes -> whoisHistory, many domains -> bulkWhoisLookup, domains by person/email/company -> reverseWhoisLookup, unregistered name -> domainAvailability. That is explicit when-to-use and when-not-to-use routing rather than implied context.

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