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

With no annotations, the description must carry behavioral disclosure, but it only states the splitting action and the absence of WHOIS/ownership data. It does not mention return format, failure behavior, or that most of the nine input parameters appear to be discarded or irrelevant.

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?

One front-loaded sentence with no filler; every word adds meaning, and the key qualifier ('without WHOIS or ownership data') is included without bloating the description.

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?

Despite a simple operation, the tool has nine optional parameters, no output schema, and no annotations, so an agent needs more context about which parameter to pass and what to expect back. The one-sentence description is not enough to resolve that ambiguity.

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 coverage is 100%, so the baseline is 3; the description adds little beyond implying the 'host' parameter is the relevant one. It does not clarify how the other eight optional parameters relate to the stated hostname-splitting purpose, but the schema already documents each parameter.

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 operation ('Split a hostname into labels') and a resource (hostname), and the qualifier 'without WHOIS or ownership data' distinguishes it from enrichment tools. It does not explicitly differentiate from URL-normalization or fetch siblings, and the nine-parameter schema introduces ambiguity about scope, so it is not a perfect 5.

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?

There is no explicit guidance about when to use domain-shape versus siblings like normalize-url, browser-url-ok, or web-fetch. The phrase 'without WHOIS or ownership data' implies a limitation but does not state conditions or alternatives.

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