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

With no annotations, the description carries the full burden and does so well. It discloses the protocol (TCP/43), the library used (whoiser), a 15s timeout, and the not_applicable failure mode when registries refuse/redact queries. This goes beyond the schema and gives valuable behavioral context. A minor gap is the lack of detail on response format, but 'Returns a CheckResult' plus failure mode is sufficient.

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?

Three sentences: purpose, use case, and implementation/behavior. Every sentence earns its place. The most important information is front-loaded, and there is zero filler. This is a model of concise, structured documentation.

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 single-parameter tool with no output schema, the description is complete: it states what it does, when to use it, how it works, timeout, return type, and a key failure mode. It provides enough context for an agent to invoke it correctly without needing additional information. The sibling context doesn't require further disambiguation given the specificity.

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 input schema already describes the single 'domain' parameter comprehensively ('Public FQDN... IPs, ports, paths, and protocol prefixes are rejected'). With 100% schema coverage, the baseline is 3, and the description does not add extra parameter-level semantics beyond what the schema provides. It could have reinforced the rejection criteria, but not necessary.

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 starts with a specific verb+resource: 'Look up the registrar, creation date, expiry date, and registry statuses for a domain.' This clearly distinguishes it from sibling tools like dns_lookup and dossier_headers by naming the exact WHOIS data fields it returns. The phrase 'Core dossier check' further situates it as the foundational WHOIS tool.

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 provides a clear use case: 'Use for ownership/expiry audit.' It does not explicitly mention alternatives or when not to use it, but the context is unambiguous for an agent deciding between this and other dossier tools. Given the clear context without exclusions, a 4 is appropriate.

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