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

The description goes well beyond the annotations (readOnlyHint, openWorldHint) by detailing the protocol fallback (TCP 43 then RDAP over HTTPS), the 15-second timeout, and the exact response statuses including not_applicable, timeout, and error, with guidance on how to interpret them ('Treat not_applicable as a finding and error as unknown'). This fully discloses the tool's behavior and edge cases.

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 four sentences, each carrying essential information: purpose, use case, protocol behavior with timeout, and return format with interpretation. It is front-loaded with the core purpose and avoids any filler. The length is justified by the tool's complexity and the lack of an output schema.

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 fallback mechanisms, timeout, and multiple status codes, the description is remarkably complete. It explains the full response format, including the status field and its variants, and provides guidance on interpreting each. Since there is no output schema, the description carries the full burden of return-value explanation, and it does so thoroughly. No critical information is missing for an agent to call it correctly.

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 schema provides 100% coverage for the single domain parameter, including type, example, and rejection criteria for IPs, ports, paths, and protocols. The description adds no additional parameter-specific semantics beyond the schema, so the baseline of 3 applies. The description's focus is on behavior and output, not parameter details.

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 states a specific verb ('Look up') and resource ('a domain's registrar, creation date, expiry date and registry statuses'), which clearly distinguishes it from sibling tools like dossier_dns or dns_lookup that handle different record types. It also explicitly mentions 'Use for an ownership or expiry check,' reinforcing its purpose and differentiating it from other dossier_* tools.

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 gives an explicit when-to-use instruction ('Use for an ownership or expiry check') and explains the fallback behavior (WHOIS then RDAP), which informs the agent of the tool's process. It does not explicitly state when not to use it or name alternatives, but the purpose is distinct enough from siblings that this is clear. A 4 is appropriate because usage context is present but no explicit exclusions.

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