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

No annotations are provided, so the description carries the full burden. It only states what the tool does not do (WHOIS/ownership), but does not disclose the return format, error handling, or how it handles the various input parameters. The schema notes that 'json' is 'discarded after the check', but the tool description itself omits such behavioral details.

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 redundant words, and the core purpose is front-loaded. It is appropriately concise, though it sacrifices necessary detail about parameters and expected usage. Still, it earns a 4 for its efficient structure.

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?

Given there is no output schema and no annotations, the description needs to explain the tool's behavior more thoroughly. With four optional parameters and no clarity on how they are used or what the tool returns, the description is incomplete. It does not cover edge cases, required inputs, or the output format, leaving the agent under-informed for correct 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%, so each parameter already has a descriptive string in the schema. The tool description adds no additional parameter semantics and does not clarify how the four parameters relate to each other (e.g., alternatives or required combinations). Baseline of 3 is appropriate since the schema already documents the parameters.

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 states a clear action ('Split a hostname into labels') and explicitly excludes WHOIS/ownership data, distinguishing it from those concerns. However, the input schema includes fields like 'json' and 'zone' that are not explained by the description, creating ambiguity about the tool's actual scope. The purpose is not a tautology but is vague about how the unrelated parameters fit.

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 guidance on when to use this tool versus its siblings such as normalize-url or validate-json. The phrase 'without WHOIS or ownership data' only clarifies what it does not do, not when it should be selected. No alternatives or conditions are mentioned.

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