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

With no annotations, the description must carry the transparency burden. It discloses that the operation is label splitting and excludes WHOIS/ownership data, but it doesn't say whether any network access occurs, how invalid hostnames are handled, or what the return value looks like. This is meaningful but incomplete.

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 tight sentence with the action front-loaded and no filler. It loses a point because it is so terse that it omits essential invocation context for a nine-parameter tool, though that omission is penalized more directly in contextual completeness.

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?

This is a high-complexity tool: nine optional parameters, no required parameters, no output schema, no annotations, and a large sibling set. The one-sentence description does not tell the agent which input to pass, what the output format is, or what happens on invalid input, so it is far from complete enough for confident 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?

The input schema already documents all nine parameters with descriptions, so the baseline is 3. The tool description adds no extra parameter-level detail and does not state that 'host' is the relevant field among the nine optional properties.

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 operation and resource—'Split a hostname into labels'—and adds a useful negative scope, 'without WHOIS or ownership data,' which separates it from ownership-oriented sibling tools. It doesn't name the 'host' parameter or mention any validation behavior, so it's clear but not maximally precise.

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 when-to-use or when-not-to-use guidance and no mention of sibling tools such as normalize-url, github-repo-shape, or browser-url-ok. The 'without WHOIS or ownership data' clause hints at a syntactic scope, but an agent is left to infer when this tool beats its alternatives.

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