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

No annotations are present, so the description carries the burden of disclosing behavior. It does disclose one useful limitation—no WHOIS or ownership lookup—and implies a pure string-splitting operation. However, it does not describe the return format, what happens when multiple inputs are provided, or any side effects such as discarded data.

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 one short sentence and is front-loaded with the core use. The qualifier 'without WHOIS or ownership data' earns its place because it prevents someone from expecting lookup features. There is no filler or redundancy.

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 tool exposes 9 optional parameters, has no annotations, and has no output schema. The one-line description gives a clear action for one parameter group but not enough context for the agent to know what output to expect, how to handle non-hostname parameters, or how to construct a valid call for the broader intended behavior.

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 input schema already describes all 9 parameters (100% coverage), so the baseline is 3. The description adds almost no parameter-level meaning beyond the word 'hostname', which aligns with the 'host' property but leaves the remaining eight optional parameters unexplained by the tool description.

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 specific verb and resource: 'Split a hostname into labels' and adds a clarifying boundary ('without WHOIS or ownership data'). It is understandable, but it does not explicitly separate this tool from sibling shape/validation tools, and the nine optional schema parameters make it unclear why so many non-hostname fields exist.

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 about when to use this tool instead of a related tool such as normalize-url, web-fetch, file-path-ok, or other shape-focused tools. The phrase 'without ownership data' hints at a limitation rather than a decision rule. An agent cannot tell whether to prefer this tool over alternatives.

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