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

With no annotations provided, the description carries the full burden of behavioral disclosure. It states the core splitting behavior and the absence of ownership data, but says nothing about accepted input forms, output shape, failure modes, or side effects; given the disparate json and zone parameters, an agent cannot reliably predict behavior.

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 the active verb and object front-loaded, and no filler. The qualifier 'without WHOIS or ownership data' earns its place by setting expectations about what the tool does not provide.

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 four optional parameters, no annotations, and no output schema, so an agent needs more contextual guidance than this one sentence provides. It does not indicate which parameter to pass, what the result looks like, or whether json and zone are relevant to hostname splitting, leaving invocation genuinely ambiguous.

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 schema has descriptions for all four properties, and schema description coverage is 100%, so the schema already carries parameter-level meaning. The description adds no parameter-specific detail and does not reconcile 'hostname' with the unrelated json and zone 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 names a concrete operation ('Split a hostname into labels') and a clear resource, so an agent knows what the tool does. It also adds a negative scope ('without WHOIS or ownership data'), though it does not explicitly contrast it with sibling tools like normalise-url.

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?

There is no guidance on when to use this tool versus alternatives, nor any explicit exclusions or prerequisite conditions. The phrase 'without WHOIS or ownership data' hints at a limitation but does not tell the agent how to choose among the optional url, host, json, and zone parameters.

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