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

Annotations already declare readOnlyHint=true, openWorldHint=true, and destructiveHint=false, so safety is covered. The description adds genuine value with the data source (registry RDAP/WHOIS), the explicit credit cost of 8, and the caveat that registrant country is only shown "where it is published". It says nothing about behavior for nonexistent/redacted domains or about rate limiting or failures.

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?

A single front-loaded sentence that moves straight from what is read to what is returned and ends with cost. It wastes a few words restating "WHOIS Lookup" twice before the real content begins, but the enumerated return fields are informative rather than filler.

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 the long return-field enumeration is partly redundant, though it usefully conveys semantics. What is missing is behavioral completeness for a zero-required-parameter tool: which of domain/ip/asn drives the lookup, whether multiple may be combined, and what happens on an unregistered domain.

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 each parameter is already documented, and the baseline of 3 applies. The description actually narrows scope to "any domain" while the schema exposes ip and asn inputs, so it adds no meaning for two of the three parameters and slightly biases the agent toward domain-only use.

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 the registry's RDAP or WHOIS record") plus a concrete field list, so an agent knows exactly what comes back. It never distinguishes itself from overlapping siblings such as DomainAge, DomainExpiration, Nameservers, IPLookup, or ASNLookup, which is the only thing keeping it from a 5.

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?

There is no when-to-use guidance, no exclusion of alternatives, and no statement about prerequisites. Critically, all three parameters are optional (required = 0) and the description never says at least one of domain/ip/asn must be supplied, nor when to prefer this over the dedicated DomainAge or Nameservers tools.

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