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

With no annotations, the description carries the full behavioral burden, but it only says the tool does not provide WHOIS or ownership data. It implies a pure parsing operation, but it does not explicitly state that the tool is read-only, makes no network calls, or discards inputs—though the schema descriptions partially cover this.

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 concise sentence that front-loads the verb and resource. Every word earns its place, and the negative qualifier about WHOIS/ownership data is useful rather than filler.

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 nine optional parameters, no annotations, and no output schema, yet the description gives no guidance on how the broad input schema maps to the stated operation. An agent cannot reliably tell which parameter to supply, what the return shape is, or how irrelevant parameters are handled, making the definition incomplete for its complexity.

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 even though the tool description adds no parameter-specific detail. The schema already describes each field, but the tool-level description does not clarify why the schema contains many fields unrelated to hostname splitting or which parameter to prefer.

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 resource: 'Split a hostname into labels,' which clearly states the core operation. The qualifier 'without WHOIS or ownership data' helps distinguish it from lookup-style tools, though it does not explicitly name a sibling alternative.

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 you need hostname labels and not WHOIS or ownership data. However, it provides no explicit alternatives, no mention of which of the nine input parameters is relevant, and no guidance about the many unrelated parameters in the schema.

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