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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It mentions 'without WHOIS or ownership data', which is a negative constraint, but it does not state whether the operation is read-only, what it returns, or any side effects. For a tool with no annotation safety hints, this is a significant gap.

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 one sentence, which is concise, but it is under-specified for a tool with four parameters and no output schema. The single sentence does not earn its place because it omits essential guidance on the other inputs, making it inappropriately brief for the tool's complexity.

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 unrelated parameters, no output schema, and no annotations, the description is drastically incomplete. It does not explain how the parameters interact, which are required for the hostname-splitting operation, what the return value looks like, or any edge cases. An agent has almost no basis for correct 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?

The input schema has 100% coverage, so each parameter has a description. However, the tool description does not connect these parameters to the stated purpose. The schema descriptions themselves are generic and mismatched (e.g., 'HTTPS URL to normalize or cite' for 'url', 'JSON text to validate' for 'json'), and the description adds no meaning beyond that. An agent cannot infer how 'json' or 'zone' relate to splitting a hostname.

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 verb and resource: 'Split a hostname into labels'. This is clear and matches the tool name. However, it does not differentiate from siblings like normalize-url or citation, which may also handle hostnames, and it ignores the other three parameters (url, json, zone) that appear in the schema, leaving their purpose unexplained.

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. There is no mention of when to prefer this over normalize-url or citation, and no exclusions or conditions. The description implies a use case for hostname splitting but gives no context for the other input fields, so an agent cannot decide when to invoke it.

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