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

With no annotations at all, the description must carry the behavioral disclosure burden. It states a transformation but does not reveal side effects, read-only guarantees, rate limits, return shape, or whether it performs any external lookup. 'Without WHOIS or ownership data' only narrows the expected output; it does not describe actual runtime 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?

The description is a single efficient sentence with no filler and is appropriately front-loaded. While it could be more informative, it is definitely concise rather than over-padded.

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?

For a nine-parameter tool with no output schema and no annotations, one sentence about splitting hostnames is drastically incomplete. It does not mention return values, which parameter should be supplied, or what happens to the unused fields, so an agent cannot confidently invoke the tool correctly.

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 structured schema already explains all parameters, leaving the description with little extra to add. The mention of 'hostname' loosely implies the host parameter, but the description does not add semantic value for the other eight fields or explain how they interact.

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 action and resource: 'Split a hostname into labels'. However, the input schema lists nine unrelated optional parameters, and the description does not explain why those exist or which one the action applies to, leaving the true scope unclear. It also does not differentiate this tool from sibling shape-checking 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?

No guidance is given about when to use this tool instead of a sibling such as normalize-url, github-repo-shape, or geo-hint. The phrase 'without WHOIS or ownership data' hints at what the tool does not do, but does not say when it is preferable or what prerequisite the caller should satisfy.

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