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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds that it returns 'every domain whose current WHOIS record contains the search term', which clarifies the broad result scope, but does not disclose potential large result sets, pagination, or API key requirements beyond what the schema already states. No contradiction with annotations.

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 a single, focused sentence followed by an illustrative example. It front-loads the purpose and provides a concrete invocation without unnecessary fluff. Every element earns 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 tool with only two parameters and no output schema, the description covers the core purpose and gives an example. However, it does not mention possible large result sets, pagination, or error handling, which could be relevant for a search returning 'every domain'. The annotations cover safety, but the description leaves out behavioral details an agent might need for robust handling.

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% for both 'term' and '_apiKey', so the schema already documents the parameters. The description adds a concrete usage example and clarifies that 'term' can be an email, name, or organization, which slightly reinforces the schema's description but does not add significant new meaning.

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's function: reverse WHOIS lookup to find domains registered by a given email/name/org. It uses a specific verb ('Find') and resource ('domains'), and distinguishes itself from siblings like whoisxml_whois (direct lookup) and whoisxml_whois_history (historical) by focusing on searching by registrant information.

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 usage for finding domains by registrant info and provides an example, but does not explicitly contrast with sibling tools (e.g., whoisxml_whois) or state when not to use this tool. There is no mention of alternative tools or exclusions, so the agent must infer the use case from context.

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