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

With no annotations, the description must carry the safety and behavior burden. It does disclose that no WHOIS or ownership data is fetched, which implies a local parse, but it does not describe output format, handling of invalid hostnames, lowercasing, label order, or network 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?

One sentence, front-loaded with the action, with no filler or repeated schema content. The exclusion of WHOIS/ownership is the only necessary clarification and it earns its place.

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?

For a tool with no output schema, no annotations, and a nine-parameter optional schema, a one-sentence description is incomplete: it does not say what 'labels' means as a return value, whether the split is reversible/ordered, or how to handle invalid inputs. The mismatch between the narrow description and the broad schema also leaves invocation ambiguities.

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; each parameter has its own description, and the 'host' property clearly maps to the hostname in the tool description. The description adds no extra parameter-level detail and does not explicitly tell the agent to pass 'host' among the eight other optional fields.

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 direct action ('split a hostname into labels') and a specific resource, making the tool's core purpose obvious. The caveat 'without WHOIS or ownership data' also separates it from domain-information tools and clarifies the scope.

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 gives a clear context: use it when you need a hostname split into labels, not ownership/WHOIS enrichment. It does not name explicit sibling alternatives, but the exclusion of WHOIS/ownership is a useful when-not signal.

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