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

With no annotations, the description carries the full burden of behavioral disclosure. It discloses that no WHOIS/ownership data is returned, which is useful, but it does not state whether the tool performs network calls, how it handles invalid hostnames, which parameter is authoritative, or what the output looks like. The schema's 'json' parameter says 'discarded after the check,' hinting at behavior the description omits.

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 filler. Every word contributes to the core function and scope.

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 optional parameters and no output schema or annotations, this description is too thin. It doesn't explain the return format, the relationship between the four parameters, or the conditions under which each should be supplied. The presence of unrelated-looking parameters (json, zone) makes the missing context more damaging.

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 no parameter-level meaning beyond the schema; it doesn't clarify whether 'host' is preferred over 'url' or why 'json' and 'zone' are accepted. The schema's own descriptions are clear, but the tool-level description does not connect them to the stated purpose.

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'), a specific resource ('hostname'), and an explicit scope exclusion ('without WHOIS or ownership data'), making the core function clear. However, the input schema accepts url, json, and zone parameters that are not accounted for in the description, so the stated purpose does not fully explain the tool's interface.

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 given about when to choose this tool over siblings such as normalize-url or validate-json. The only hint is the exclusion of WHOIS/ownership data, which clarifies what the tool does not return, not when to use it. An agent has to infer that this is for hostname label splitting.

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