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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint, so the safety profile is covered. The description adds genuinely useful behavior beyond that: redacted:true is the post-GDPR norm rather than a failure, `unknown` means the registry did not answer (not absence), and `reason` distinguishes rate limit, timeout, registry error, or no RDAP service. The flat 'Observation only, report never advise' framing is the one place the description restates the read-only guarantee the annotations already make, so the score lands just under 4.

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?

Front-loaded with the trigger, then the payload, then the status semantics, then the sibling routing — a logical order with no wasted sentences. It is dense and runs long for a one-parameter tool, and the 'REPORT, never advice to buy' line is more prescriptive than informative, keeping it off a 5.

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?

Return values are largely covered by the output schema, yet the description still supplies the interpretive keys an agent needs (`status` tri-state, `reason`, `redacted`) and the hard rule never to call a name free unless status is exactly not_registered. For a single-parameter read tool this leaves no meaningful gap.

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% for the single `domain` parameter, and the schema itself already documents bare names, subdomains, rejection of scheme/path/port, and punycode normalization. The description adds no format or validation detail beyond that, so the baseline 3 applies.

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 and resource (reads a domain's registration from the registry over RDAP) and immediately enumerates the exact questions it answers — owner, expiry, registrar, nameservers, registered status, transfer/delete locks. It is clearly separable from siblings like check_domain_names and check_domain_verification.

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?

Opens with an explicit when-to-use trigger ('when the user asks who owns a domain... the WHOIS question') and names the alternative for the multi-name case: call check_domain_names once with up to 20 names instead of this tool per name. Both the selecting condition and the exclusion are stated.

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