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

With no annotations, the description must carry behavioral weight; it does disclose that the tool will not perform WHOIS/ownership lookup and implies a pure local split. However, it does not mention how irrelevant parameters are handled, whether a valid hostname is required, or any error/edge-case behavior.

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?

A single front-loaded sentence with no filler; verb and object appear first and the WHOIS exclusion is a useful qualifier. This is appropriately concise.

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 a well-covered schema, the description alone leaves the agent unsure of the primary parameter, output format, and error behavior, especially since the schema contains many seemingly unrelated optional params. No output schema or annotations exist, so the terse description is insufficient for confident use.

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%, with property descriptions like 'Public hostname' and 'discarded after the shape check' already documenting each parameter. The tool description adds no extra param semantics beyond identifying hostname as the input concept, so the baseline 3 applies.

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 names a concrete operation ('split a hostname into labels') and states a clear non-goal ('without WHOIS or ownership data'), so the core purpose is understandable. It does not explicitly contrast with sibling tools, but the hostname scope separates it from URL/path/JSON tools.

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 statement of when to prefer this tool over siblings, no example trigger, and no mention of alternatives. The negative scope is the only hint, which is insufficient guidance for an agent deciding among many shape/URL tools.

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