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

No annotations are present, so the description carries the full behavioral burden. It adds one useful negative ('without WHOIS or ownership data'), but it does not disclose whether the tool performs network access, what happens to the input parameters, or the shape of the result, which is a significant gap for a no-annotation tool.

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?

A single sentence with no wasted words; the core operation is front-loaded and the caveat about WHOIS/ownership follows immediately.

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 output schema and no annotations, the description needs to communicate return values and invocation expectations, but it only states a basic operation. The nine optional parameters and sibling tools make the one-sentence description insufficient for confident invocation.

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's 'hostname' points toward the `host` property, but it adds no detail on format, requiredness, or how the other eight optional parameters relate to the operation.

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', and the 'without WHOIS or ownership data' clause makes clear this is a purely lexical operation, not a domain lookup. It does not name sibling shape tools, but the hostname scope is unambiguous enough to distinguish it.

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?

It gives a direct, clear context for use: an agent should reach for this tool when it needs hostname labels, and the 'without WHOIS or ownership data' boundary warns against using it for ownership info. It stops short of a 5 because it never names alternatives such as normalize-url or browser-url-ok.

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