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

With no annotations, the description carries the full burden, but it only discloses the absence of WHOIS/ownership data. It does not mention output shape, whether any validation or normalization occurs, side effects, error behavior, or how the json and zone parameters are used. Minimal transparency beyond the core action.

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; the limiting clause 'without WHOIS or ownership data' earns its place. It is concise, though the brevity omits important operational context, so it falls just short of a perfect structure score.

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?

For a tool with four heterogeneous parameters, no output schema, and no annotations, the one-sentence description is not complete. It does not state which parameter is canonical, what the tool returns, or how it compares to siblings like normalize-url and validate-json. An agent would struggle to invoke it correctly.

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 tool description adds no parameter-level meaning beyond the schema; it only references 'hostname' while the schema also includes url, json, and zone with no explanatory link. The schema does the work here.

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 ('split') and resource ('hostname'), and the phrase 'without WHOIS or ownership data' helps distinguish this tool from potential domain lookup alternatives. However, it does not reconcile the unrelated url/json/zone parameters in the schema, leaving some ambiguity about the tool's full scope.

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 gives no explicit guidance on when to use this tool versus siblings like normalize-url or validate-json. The only hint is the negative clause 'without WHOIS or ownership data,' which sets a boundary but does not tell an agent the preferred selection conditions.

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