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

With no annotations, the description must disclose behavior, but it only states a pure function without side effects, return format, or error behavior. Parameter descriptions mention 'discarded after the shape check' which implies validation logic, but the tool description does not elaborate, leaving behavior opaque.

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 extremely concise (one sentence), which is structurally fine. However, it is too terse to convey necessary information, balancing brevity with a lack of substantive content.

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 9 parameters and no output schema, the description fails to provide essential context about the tool's operation, parameter roles, or expected results. An agent would have no way to correctly invoke this tool based solely on the provided information.

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 descriptions cover all 9 parameters, but many (e.g., 'ref', 'city', 'query') are unrelated to hostname splitting, suggesting the tool may be misnamed or repurposed. The tool description adds no clarification on how parameters relate to the stated action, so the semantics remain confusing.

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') but the parameter list includes many unrelated fields (e.g., 'ref', 'city', 'query'), making the actual purpose ambiguous. The phrase 'without WHOIS or ownership data' gives a slight hint but does not clarify why so many parameters exist.

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 provided on when to use this tool versus alternatives. The description merely notes what it does not do ('without WHOIS or ownership data'), but there is no explicit instruction on selection criteria or context of use.

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