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 does add a useful negative: the tool does not return WHOIS or ownership data. But it does not explain how the url, json, or zone inputs behave, whether the operation is read-only, what the output format is, or whether inputs like JSON are discarded.

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 no filler and the core action is front-loaded. It is efficient, though arguably too terse for a tool whose schema includes four heterogeneous optional parameters. The conciseness itself is good, but it comes at the cost of completeness.

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 spanning hostname, URL, JSON, and timezone concepts, no output schema, and no annotations. The description only addresses hostname label splitting, leaving url normalization/citation, JSON validation/discarding, and timezone behavior entirely unexplained. An agent cannot reliably determine what this tool does with the other input types.

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 even though the tool description adds no parameter-level meaning. The description and schema are only loosely aligned: 'hostname' maps to the 'host' parameter, but the url, json, and zone parameters are unexplained by the description. The schema itself documents them, so the description neither harms nor substantially helps parameter understanding.

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 and resource: 'Split a hostname into labels.' The qualifier 'without WHOIS or ownership data' helps distinguish it from ownership-related domain tools. However, the schema contains url, json, and zone parameters that the description does not account for, so the stated purpose is clear but incomplete relative to the full parameter surface.

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 use this tool versus siblings such as normalize-url, validate-json, or iana-zones. The exclusion of WHOIS/ownership data is a small hint, but there is no explicit when-to-use or when-not-to-use guidance, nor any mention of the url/json/zone variants.

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