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

No annotations are provided, so the description must disclose behavior on its own. It explains what data the tool omits, but not what it returns, how it handles the four different inputs, or whether it performs any validation or transformation beyond splitting.

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 filler, and the main behavior is front-loaded. The phrase 'without WHOIS or ownership data' earns its place by setting expectations, though the brevity leaves some contextual gaps.

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, this description is too sparse to fully guide invocation. It does not explain how the parameters relate to the operation or what result an agent should expect, leaving significant room for misinterpretation.

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 input schema already documents url, host, json, and zone. The tool description adds no parameter-level meaning and actually creates ambiguity by talking only about hostname splitting while the schema lists unrelated optional 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 operation: 'Split a hostname into labels', which is specific and actionable. It also adds a useful boundary by saying 'without WHOIS or ownership data', which helps distinguish it from enrichment-style domain tools.

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 implies when to use the tool: when hostname labels are needed and WHOIS or ownership data is not. However, it does not explicitly state when not to use it or point to sibling alternatives, so the guidance is more implicit than explicit.

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