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

Annotations are absent, so the description must fully disclose behavior, but it only covers the core splitting action and the WHOIS exclusion. It does not explain how the other parameters (especially json, which the schema says is 'discarded') are treated, nor anything about return values or side effects.

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 front-loaded sentence with no wasted words, and the 'without WHOIS or ownership data' qualifier is genuinely informative. The brevity hurts completeness, but the sentence structure itself is efficient.

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?

With four optional parameters, no output schema, and no annotations, the description fails to explain the tool's broader behavior. It leaves the purposes of url, json, and zone largely unaddressed and does not describe the expected output format, making it insufficient for reliable 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 the baseline is 3. The description adds meaning only by clarifying the 'host' parameter's purpose (hostname labels), while offering no additional context for url, json, or zone beyond the schema's own descriptions.

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 action, 'Split a hostname into labels', and adds a useful exclusion ('without WHOIS or ownership data'). However, it conflicts with the input schema, which includes unrelated parameters like url, json, and zone, making the tool's actual purpose unclear beyond the narrow hostname-splitting claim.

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 negative scope ('without WHOIS or ownership data') implies when the tool should or should not be used, but no explicit guidance or alternative tools are mentioned. The agent must infer the usage boundary from that single phrase.

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