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

No annotations are present, so the description carries the full burden. It discloses one useful behavioral fact—no WHOIS/ownership lookup—but does not state return format, error behavior, normalization, or whether invalid hostnames raise errors. For a pure parser this is incomplete transparency, though not contradictory.

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?

One sentence, front-loaded with the action, and the exclusion clause earns its place by distinguishing the tool from WHOIS/ownership tools. No fluff or repetition of schema details.

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?

Given no annotations, no output schema, and a nine-property schema that mostly appears irrelevant to domain splitting, the description is not complete enough for an agent to reliably invoke the tool. It does not specify which parameter(s) to pass, whether other fields are ignored, or what the response looks like. The name and one-line description leave too much to inference.

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 for this dimension is 3. The description adds a slight hint that the relevant parameter is host, but with nine optional parameters and no required field it does not resolve which values the tool consumes or what happens to the others. Thus it does not exceed the baseline.

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?

States a specific verb and resource: 'Split a hostname into labels' and adds a boundary by excluding WHOIS/ownership data. This makes the core purpose clear and separates it from lookup-style tools. However, the input schema lists eight other unrelated optional fields (city, feed, json, path, zone, query, etc.), which blurs which input the tool actually operates on.

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 when-to-use guidance and names no alternatives from the sibling list (e.g., normalize-url, browser-url-ok, github-repo-shape). 'Without WHOIS or ownership data' is only a negative boundary, not actionable direction about when to choose this tool or what to use instead. An agent must guess the decision criteria.

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