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

With no annotations provided, the description carries the full burden of behavioral disclosure. It explains the core operation and what is not included, but it does not disclose whether the tool accepts arbitrary hosts, what happens with invalid input, whether there is any network dependency, or what the returned label structure looks like. The discard semantics scattered through the schema partially compensate, but those are schema details, not description content.

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, front-loaded sentence with no filler. Every word conveys scope: the action, the input type, and the exclusion of WHOIS/ownership data. It is appropriately sized for a focused utility.

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?

Despite the simple phrasing, the tool has nine optional parameters, no output schema, no annotations, and many sibling tools with similar naming patterns. The description does not explain which parameters are relevant, what the return format is, or how to handle edge cases. This is not complete enough for an agent to reliably select and invoke the tool correctly in all contexts.

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. The tool description itself adds no parameter-level meaning, but the schema already documents parameters like 'host' and notes that many are discarded after a check. The description is consistent with using 'host', though it does not explicitly map the operation to that parameter or clarify why several unrelated parameters exist.

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 and resource: 'Split a hostname into labels'. The 'without WHOIS or ownership data' clause clarifies scope and helps distinguish it from lookups that return ownership information. However, it does not explicitly differentiate itself from sibling shape-checking tools such as github-repo-shape or figma-url-shape.

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 no guidance on when to use this tool versus alternatives, and no exclusions or prerequisites are mentioned. An agent must infer from the name and the host parameter that it is meant for hostname parsing. There is no mention of when another sibling tool would be more appropriate.

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