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

No annotations are provided, so the description carries the full behavioral burden. It does disclose that no WHOIS or ownership data will be fetched, which is useful. But it does not describe the return format, behavior on invalid hostnames, or what happens when non-host parameters such as url, city, json, or zone are supplied. Given the broad optional schema, this transparency gap is significant.

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 or repetition. The core behavior and a key scoping constraint are front-loaded, and every word contributes to the tool's meaning.

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 no output schema and no annotations, yet it exposes nine optional parameters and sits among many related sibling tools. A one-line description of hostname splitting is not enough for an agent to invoke it reliably, because it omits the return shape, how to select the right parameter, and when to prefer this tool over similar ones.

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 already documents all nine parameters, so the baseline is 3. The description adds essentially no parameter-level meaning beyond loosely aligning 'hostname' with the `host` property. It doesn't indicate whether `host` is the relevant argument or whether the other fields are alternatives or ignored.

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 names a specific operation ('split') and resource ('hostname'), and specifies the result ('labels'). The qualifier 'without WHOIS or ownership data' distinguishes it from ownership lookups. It loses a point because the input schema exposes nine unrelated optional parameters, and the description doesn't clarify how they fit with the stated hostname-splitting purpose.

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 description implies the tool is for pure hostname label decomposition and explicitly rules out WHOIS or ownership data. However, it names no sibling alternatives or conditions for choosing this tool over related tools like normalize-url, browser-url-ok, or web-fetch. It also doesn't say which input parameter should be populated.

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