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

Goes beyond the readOnly/idempotent annotations by disclosing the data path ("read live from the registry's own record (RDAP, else WHOIS)"), the privacy boundary ("Never owner details"), and the access model ("Free, no sign-in"). It also flags the derived signals — estimated drop date and Ahrefs Domain Rating — so the agent knows what it will and won't get.

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 verb and the returned fields, with caveats (never owner details, free, no sign-in) kept short. The run-on field list and the quoted-example tail are slightly bloated but still earn their place as disambiguators.

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?

An output schema exists, so return structure needn't be re-explained, and the description still covers source, privacy, auth, and the bonus DR field. The only gap is the missing guidance on overlapping siblings and on failure modes for unregistered domains.

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 domain property already documents that a link is accepted, so the description only adds the phrase "any domain." It provides no syntax, normalization, or error-behavior detail beyond the schema baseline.

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 ("WHOIS / RDAP lookup for any domain") and enumerates exactly which fields it returns. It is clearly separable from siblings like domain_rating and check_domain because it names registry data as the core payload.

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 trailing quoted queries ("whois heya.page", "how old is this site", "is this domain expiring") give concrete triggers that map user phrasing to this tool. However it never says when to prefer check_domain or domain_rating instead, and the DR overlap with the domain_rating sibling is left unexplained.

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