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

With no annotations present, the description carries the full disclosure burden, but it only reveals that the tool does not consult WHOIS or ownership data. It does not state whether the operation is read-only, what it returns, how invalid input is handled, or how the many non-host parameters are treated. The schema's 'discarded' notes add some context, but they are outside the description itself.

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 an active verb and no filler. It loses a point because its brevity omits the tool's broader input surface, making it concise but under-explanatory relative to the actual schema.

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 has nine optional parameters, no output schema, and no annotations, so the description must explain the general input model and expected behavior. It only addresses `host`, leaving the other eight properties unexplained at the description level, and it never states whether parameters should be used individually or in combination. The schema descriptions help, but the overall contract is too incomplete for reliable agent selection.

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 even though the description adds no parameter-level detail. The schema already explains each optional property, such as `json` being 'JSON text to validate; discarded after the check.' The description's mention of hostname maps only to `host` and provides no additional semantic value beyond the schema.

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 ('Split a hostname into labels') and an exclusion ('without WHOIS or ownership data'), so it is not a tautology. However, it covers only one of the nine input properties in the schema (`host`), leaving `url`, `json`, `path`, `query`, and others unaddressed. The tool's actual scope is therefore ambiguous: it reads like a hostname-only parser while the schema suggests a broader shape-validation utility.

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 phrase 'without WHOIS or ownership data' implies a boundary around pure shape parsing, but the description never states when to choose this tool over siblings like `normalize-url`, `browser-url-ok`, `file-path-ok`, or `validate-json`. No alternatives, exclusions, or explicit conditions are given. The intended usage is only inferred from the verb 'split a hostname.'

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