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 a hostname into labels' and 'without WHOIS or ownership data' – it does not disclose how it handles the other eight parameters, whether it validates them, what it returns, or any side effects. The parameter descriptions mention 'discarded after the check', but the tool description itself omits this, leaving behavior largely opaque.

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. It is efficient and wastes no words, though it is perhaps too terse to convey the tool's full scope. Structurally, it is acceptable for a short utility.

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 9 parameters, no annotations, and no output schema, the description is severely inadequate. It does not explain which parameters are relevant to the stated purpose, how the tool behaves for non-hostname inputs, what the output looks like, or any edge cases. The agent has almost no guidance for correct invocation, making the tool nearly unusable based on this definition.

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 each parameter has a description. The tool description itself adds no parameter-level meaning beyond what the schema provides; it only refers to hostname splitting, while the schema already documents each field's purpose. Since coverage is full, the baseline of 3 applies; the description does not compensate or enrich parameter semantics.

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 clearly states the primary action: splitting a hostname into labels, and explicitly disclaims WHOIS/ownership data. This distinguishes it from URL-normalizing siblings like normalize-url, though it does not mention that the tool also accepts many unrelated parameters, which could confuse the agent about the tool's true 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 gives no explicit guidance on when to use this tool over alternatives. It only notes what it does not do (no WHOIS/ownership), but doesn't mention sibling tools like normalize-url or browser-url-ok, nor does it state any conditions for selecting this tool. The lack of exclusionary or alternative guidance leaves the agent to guess.

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