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

With no annotations, the description carries the full burden of behavioral disclosure. It only says 'split into labels' and 'without WHOIS or ownership data'; it does not mention the output format, error behavior, whether network/DNS calls occur, or that unrelated schema parameters are discarded.

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. The verb and resource are immediate, and the WHOIS/ownership exclusion is a useful, concise clarification.

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 description is too thin given the lack of annotations, lack of an output schema, and a nine-parameter optional schema. An agent cannot tell what the tool returns, which parameter to use, or how this relates to the many sibling shape/check tools, so reliable invocation is not well supported.

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 description adds no parameter-level meaning, such as clarifying that 'host' is the relevant field among the nine optional parameters, but the schema already documents each parameter adequately.

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 action and resource: 'Split a hostname into labels' and scopes out WHOIS/ownership data. This is clear and distinguishes from a WHOIS/ownership lookup, but it does not contrast with sibling URL/hostname tools like normalize-url or browser-url-ok.

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 guidance on when to use this tool versus alternatives, no exclusion criteria, and no mention of which of the nine optional parameters should be supplied. The description leaves the agent to infer the intended usage entirely.

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