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

With no annotations, the description must carry the behavioral disclosure burden. It does disclose one limitation (no WHOIS or ownership data), but it says nothing about return values, side effects, or what happens to the many other accepted parameters such as ref, url, city, json, path, and query. The schema's per-parameter 'discarded after' notes help, but the tool description itself is too thin.

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 single sentence is compact and the 'without WHOIS or ownership data' qualifier earns its place. But for a tool with nine optional parameters, no annotations, and no output schema, the description is under-specified rather than appropriately sized.

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 high contextual complexity: nine optional parameters, no annotations, and no output schema. The description covers only the hostname-label use case and leaves the agent unable to predict what result to expect, which parameter to pass, or how this tool relates to its many shape/ok siblings.

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. The description adds no parameter-level meaning beyond the word 'hostname', and it does not explain how the other parameters relate to the described behavior.

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 object: 'Split a hostname into labels', and adds a meaningful boundary ('without WHOIS or ownership data') that distinguishes it from enrichment tools. However, the input schema exposes eight other unrelated optional parameters, so the description does not fully clarify the tool's actual 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?

It provides a clear use context: use this when you need hostname labels only. The qualifier 'without WHOIS or ownership data' implies a boundary, but no alternative tool is named and no explicit when-not-to-use guidance is given, leaving sibling tool selection mostly to inference.

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