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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the safety profile is covered. The description adds behavioral context by specifying what kind of data is returned—past registrars, registrants, and dates—which helps set expectations beyond the annotations without contradicting them.

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 two sentences and includes a complete invocation example. It front-loads the core purpose and avoids filler, with every element earning its place.

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 simple two-parameter lookup tool, the description is largely complete: it names the inputs, shows an example, and describes the kind of output to expect. Since there is no output schema, a bit more detail about the response structure (e.g., whether it returns a list of records) would make it fully complete, but the current level is sufficient for correct invocation.

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 both domain and _apiKey. The description's example repeats the parameter names but adds no new semantic information beyond what the schema provides, which fits the baseline of 3.

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 clearly states the tool returns historical WHOIS records for a domain, enumerating the specific data points: past registrars, registrants, and creation/expiry dates. The word 'historical' and 'over time' distinguish it from sibling tools like whoisxml_whois, which implies current WHOIS data.

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 implies use when historical WHOIS information is needed, but it does not explicitly state when to prefer this tool over whoisxml_whois or whoisxml_reverse_whois. No alternative tools or exclusion conditions are mentioned, so the agent must infer usage context from the word 'historical'.

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