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

With no annotations, the description must carry the behavioral disclosure burden, but it only covers label splitting. It does not explain how the schema's four parameters (url, host, json, zone) are used, which is authoritative, or what the output looks like.

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 that front-loads the core action and includes a useful scoping caveat. It contains no filler, though its brevity contributes to the missing behavioral context.

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 four heterogeneous parameters, no output schema, and no annotations, yet the description offers no output format, no parameter prioritization, and no usage context. This is too sparse for an agent to invoke confidently without additional inference.

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 baseline of 3 applies. The description adds no parameter-specific meaning and arguably misaligns with the schema, which accepts json and zone in addition to hostname-related inputs.

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 specific operation — 'split a hostname into labels' — and explicitly scopes out WHOIS/ownership data, which helps distinguish it from ownership-oriented domain tools. It is clear and actionable, though it does not position itself relative to the actual sibling tools like normalize-url or validate-json.

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?

No guidance is given for when to prefer this tool over alternatives. The caveat 'without WHOIS or ownership data' implies it is not for ownership lookups, but sibling tools are never mentioned, so an agent must infer the selection logic.

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