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

Annotations are absent, so the description must carry the full burden of behavioral disclosure. It only states that the tool does not return WHOIS/ownership data, which is a useful constraint, but it says nothing about the output format, which parameter is consumed, or what happens when multiple parameters are provided. For a tool with no output schema, this is insufficient for an agent to predict the result.

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 that leads with the primary action ('Split a hostname into labels') and then adds a relevant caveat. There is no fluff, and the core purpose is front-loaded. However, it may be too brief for the complexity of the tool, but that is a completeness issue rather than a conciseness one.

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?

With no annotations, no output schema, and a minimal description, the agent lacks essential context: which parameter to pass, what the return structure looks like, and how the optional 'json' and 'zone' parameters behave. Given the tool has 4 optional parameters and a specific action, this level of description is inadequate 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 schema descriptions for all four parameters are complete (100% coverage), so the baseline is 3. The tool description does not add any meaning beyond what the schema already provides; it does not clarify how 'url' or 'host' relates to the splitting action, nor what 'json' or 'zone' are used for. It adds no value but also does not mislead.

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 clearly states the primary function: 'Split a hostname into labels.' It also adds a differentiator by noting it does so 'without WHOIS or ownership data,' which helps distinguish it from potential domain-investigation tools. However, it does not explicitly name which parameter (url vs host) is the intended input, leaving some ambiguity for the agent.

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 its siblings, such as normalize-url or validate-json. It neither states prerequisites nor mentions alternatives, so an agent has to infer from the tool name and schema alone. This is a significant gap given the diverse set of sibling tools.

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