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

With no annotations provided, the description must carry the behavioral disclosure burden. It does disclose that the tool does not include WHOIS or ownership data, which is a useful limitation. However, it does not describe side effects, what happens with non-hostname inputs (e.g., json or zone), or the return format, leaving gaps in behavioral transparency.

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, concise sentence that front-loads the core action ('Split a hostname into labels') and adds a key limitation. There is no wasted wording, and it is appropriately sized for a simple tool.

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 the tool has 4 diverse parameters (url, host, json, zone) and no output schema, the description is too narrow. It only explains the hostname-splitting function, leaving the purpose and handling of the other parameters unexplained. Without annotations or output schema, this incompleteness makes it hard for an agent to correctly invoke the tool for non-hostname inputs.

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 description coverage is 100%, so each parameter already has a clear description. The tool description adds minimal parameter context—only implying that 'hostname' is relevant. Since the schema covers the parameters thoroughly, the baseline of 3 is appropriate; the description does not significantly enhance parameter understanding.

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 uses a clear verb ('split') and resource ('hostname into labels'), and explicitly states the exclusion of WHOIS/ownership data, which helps distinguish it from potential ownership-related tools. However, it does not mention that the tool accepts multiple input types (url, host, json, zone) from the schema, so it is not fully precise about its scope.

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 no guidance on when to use this tool versus sibling tools like normalize-url or validate-json. It does not state prerequisites, alternatives, or conditions for selecting this tool over others, leaving the agent to infer usage.

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