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

No annotations are provided, so the description carries the behavioral disclosure burden. It does disclose one meaningful boundary—no WHOIS or ownership enrichment—but it does not say whether the tool performs network calls, how malformed hostnames are handled, or what the exact return structure is. The schema's 'discarded' notes add some behavioral context, but the tool description itself is thin.

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 sentence with no filler, and the main action is front-loaded. The 'without WHOIS or ownership data' clause earns its place by setting expectations. It is concise, though the terseness leaves some clarity gaps noted elsewhere.

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?

The tool has no output schema and no annotations, and the description only hints at the return value by saying 'split into labels.' It does not explain the output format, error behavior, or which of the nine optional parameters are actually relevant to the described operation. This is minimally viable but not complete enough for an agent to invoke with confidence beyond the obvious `host` case.

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 baseline is 3 and the description does not need to re-document parameters. The description's 'hostname' maps conceptually to the `host` parameter, but it adds no parameter-level detail beyond what the schema already provides. The relationship between the stated hostname operation and the other eight optional parameters is never clarified.

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 clear action ('split a hostname into labels') and a specific resource (hostname), and the 'without WHOIS or ownership data' clause adds useful scoping that distinguishes it from domain-lookup tools. It does not explicitly name a sibling alternative, so it is not a perfect 5, and the nine-parameter schema includes many unrelated fields that the description does not acknowledge.

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?

There is no explicit guidance about when to use this tool instead of a sibling shape/validation tool. The only hint is the negative clause 'without WHOIS or ownership data,' which describes what the tool does not do rather than when to select it. An agent would have to infer the intended use from the tool name alone.

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