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

The description discloses a useful behavioral trait beyond the schema: the tool performs no WHOIS or ownership lookup, which implies a local, read-only split operation. Given that no annotations are provided, this helps, but the description still does not mention that other schema parameters appear to be discarded or what the return shape is.

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 action and limitation. It is concise, though a second sentence clarifying the multi-parameter schema would have made it more complete.

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 9-parameter optional schema, the one-line description is insufficient to fully define the call contract. It does not identify which parameter to populate beyond the implicit 'host', does not describe the return value, and does not explain why unrelated parameters like city, json, path, and zone are present or ignored.

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 covers all 9 parameters with descriptions, so the baseline is 3. The description's 'hostname' maps naturally to the 'host' parameter, but it adds no additional parameter semantics such as precedence, formatting, or discard behavior beyond what the schema already states.

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 clear negative scope ('without WHOIS or ownership data') that distinguishes it from ownership/WHOIS lookups. It does not explicitly name a sibling alternative, so it is not a 5, but the core action is unambiguous.

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?

The phrase 'Split a hostname into labels' implies when to use it, and the 'without WHOIS or ownership data' clause tells the agent not to expect ownership information. However, there is no explicit when-to-use vs. when-not-to-use guidance and no alternative tool is named, leaving some inference required.

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