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

Annotations already cover read-only, idempotent, open-world and non-destructive semantics, so the description's added value is in what is returned (field list) and where the data comes from (registry-sourced, not a cached WHOIS mirror). It also discloses the negative-result shape ('registered: false'), which is genuinely useful for branching logic. It does not mention rate limits or behavior for TLDs lacking an RDAP endpoint.

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?

Roughly two sentences, front-loaded with the intent question, then the field inventory and the negative case. Telegraphic but every clause carries information and nothing is repeated from the schema or annotations.

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?

One required parameter and no output schema, so the description correctly carries the return-value burden by listing fields and the not-registered outcome. Slightly short of complete because error/edge behavior (unsupported TLD, rate limiting) is unstated.

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% and the single parameter already documents normalization of URLs/subdomains to the registered name, so the description adds no parameter-level meaning. Baseline 3 applies per the schema-coverage rule.

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?

Names a specific verb+resource ('RDAP registration data for a domain') and enumerates exactly what comes back: created, updated, expires, age in days, registrar, status, nameservers, DNSSEC. It also names the data provenance (TLD registry located via IANA bootstrap), which no sibling tool (company_lookup, lei_lookup, vat_check) covers.

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 leading question 'Who registered this domain and when?' frames the use case clearly, and 'Or registered: false' tells the agent the tool is also an availability check. No explicit exclusions or alternatives are given, but no sibling overlaps this resource, so the gap is minor.

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