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

Annotations already declare readOnlyHint=true and openWorldHint=true, covering the safety and external-data profile. The description adds specificity about the returned fields (ownership, registrar, expiration) but doesn't disclose any caveats like rate limits or privacy redaction, which would be valuable for a WHOIS lookup. Thus a 3.

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 22 words, with the primary action front-loaded. Every sentence contributes: the first states what it does, the second states when to use it.

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 one-parameter read-only tool with no output schema, the description adequately conveys the purpose and the type of data returned (ownership, registrar, expiration). It doesn't mention output format or common WHOIS limitations, but the simplicity and annotations keep it reasonably complete.

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?

The single 'domain' parameter is fully described in the schema ('Domain name to look up'), achieving 100% schema coverage. The description doesn't add any additional syntax, format, or normalization guidance for the domain parameter, so it stays at the 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?

The description clearly states a specific verb ('Get') and resource ('WHOIS registration data for a domain'), and enumerates the key data types (ownership, registrar, expiration date), which distinguishes it from sibling lookup tools like lookup_dns or lookup_ssl.

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 explicitly says 'Use when you need to find domain ownership, registrar, or expiration date', providing clear context for when to invoke this tool. It doesn't mention exclusions or alternatives, so it falls short of a 5.

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