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

With no annotations provided, the description carries the behavioral burden. It clearly states what the tool does and, importantly, what it does not do ('without WHOIS or ownership data'), implying no ownership lookup or network fetch. This is adequate for a simple parsing utility, though output details are not explicitly disclosed.

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 sentence with no filler. It front-loads the action and adds a meaningful boundary in the second clause. Every word contributes to selection and invocation.

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 and no annotations, and the input schema allows nine optional parameters without indicating which one is the primary target. The description implies 'host' as the relevant parameter and implies the return value is labels, but it does not explicitly state the output format or confirm how unrelated parameters are handled, leaving some ambiguity for invocation.

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%, and each parameter is described in the schema, including that most values are 'discarded' after a check. The main description adds little parameter-level meaning beyond naming 'hostname,' but the schema itself documents the parameters well enough for a baseline score.

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.' It also adds a differentiating constraint, 'without WHOIS or ownership data,' which distinguishes this from lookup-style tools and signals it is a pure shape/parsing 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 description implies when to use the tool: when a hostname needs to be split into labels and no ownership/WHOIS information is desired. However, it does not explicitly name alternatives, exclusions, or conditions for preferring sibling tools such as normalize-url or github-repo-shape.

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