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 only states that the tool avoids WHOIS/ownership data; it says nothing about side effects, permissions, rate limits, invalid input handling, or return behavior. The 'json' parameter's 'discarded after the check' behavior appears only in the schema, not in the description.

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, compact sentence that is front-loaded and easy to parse. It avoids fluff and clearly states the core action. However, given the breadth of the schema, a bit more structure or expansion would improve completeness without harming conciseness.

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 four optional parameters of widely different types, no annotations, and no output schema, the description is not complete. It covers only the hostname-splitting aspect and leaves the purpose of url, json, and zone unexplained, so an agent cannot confidently predict the tool's full behavior or return values.

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 description adds minimal meaning beyond the schema: it connects to 'host' but does not explain how url, json, or zone relate to the tool's behavior. The schema already documents each parameter, so the description does not need to repeat that, but it also does not clarify the mismatched parameter set.

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') and adds a useful exclusion ('without WHOIS or ownership data'). However, the input schema includes url, json, and zone parameters that are unrelated to hostname splitting, so the description leaves the tool's overall purpose ambiguous and may only describe one of several behaviors.

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 about when to use this tool versus alternatives. The phrase 'without WHOIS or ownership data' hints at a constraint but does not explain when to select this tool, what prerequisites exist, or how it differs from sibling tools.

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