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

With no annotations, the description carries the behavioral burden; it does state a meaningful trait by excluding WHOIS/ownership data. It does not, however, disclose in the description that inputs are discarded after the shape check (that appears only in property descriptions), nor does it describe side effects or output 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 one short sentence with no filler, and the main operation is stated first. It earns its place, though the extreme brevity leaves room for more parameter/usage context.

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 no output schema, no annotations, and nine optional parameters, yet the description only discusses hostname splitting. An agent gets no guidance on why the other parameters exist, whether exactly one should be provided, or what the return value looks like, so the context is incomplete.

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 schema already documents all nine parameters and their discard behavior. The tool description adds only that 'hostname' maps to the host parameter, making its additional semantic value marginal; the baseline of 3 is appropriate.

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 specific verb and resource ('Split a hostname into labels') and adds a distinguishing boundary ('without WHOIS or ownership data'), which separates it from sibling URL/status tools. However, the tool's schema admits eight other parameter types (url, json, city, etc.) with no explanation in the tool description, so the stated purpose is narrower than the actual interface.

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 use case boundary: choose this when you do not need WHOIS/ownership enrichment. But it does not explicitly name alternatives or state when to prefer sibling tools such as normalize-url or browser-url-ok, so the guidance is implied rather than explicit.

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