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

Annotations already declare readOnlyHint=true, openWorldHint=true, idempotentHint=true, destructiveHint=false. The description adds critical behavioral context beyond those: 'Observation only: no record is composed,' 'redacted: true is the post-GDPR norm, not a failure,' and the meaning of status=unknown ('NOT absence — the registry did not answer, and reason says whether that was a rate limit, a timeout, a registry error, or a TLD with no RDAP service'). This is exactly the kind of non-obvious behavior an agent needs to know.

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 dense but every sentence earns its place. It front-loads the trigger conditions, then the data returned, then the behavioral caveats. It is longer than the HIGH calibration example, but the tool's semantics (RDAP, GDPR redaction, unknown status) genuinely require this much explanation. 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?

For a single-parameter read-only tool with a rich output schema, the description covers everything an agent needs: what the tool returns, how to interpret redaction, how to interpret unknown status, and what not to do with the results. The output schema exists, so return-value details need not be repeated. The sibling list confirms this tool is the WHOIS/RDAP specialist, and the description makes that role unambiguous.

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%, so the schema already documents the domain parameter well. The description adds value by clarifying that bare registrable names and subdomains both work, that scheme/path/port do not belong, and that Unicode names are normalized to punycode. This goes beyond the schema's own description, so a 4 is warranted.

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 opens with a specific verb ('Read a domain's registration from the registry over RDAP') and enumerates the exact data returned: registrar, dates, EPP status codes, nameservers, DNSSEC flag, abuse contact. It also explicitly frames the tool as the answer to 'the WHOIS question,' which distinguishes it from sibling tools like check_record or scan_domain. This is a model of purpose clarity.

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 gives explicit when-to-use guidance: 'Use this when the user asks who owns a domain, when it expires, which registrar or nameservers it has, whether it is registered, or whether a transfer or delete lock is set.' It also provides exclusions: 'Never tell anyone a name is free unless status is exactly not_registered' and 'pendingDelete or a near expiry is something to REPORT, never advice to buy.' This is strong usage guidance.

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