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

With no annotations, the description carries the full behavioral disclosure burden. It states the core operation and an important exclusion, but does not disclose return format, network behavior, side effects, or which input is actually consumed. This is adequate for a simple pure function but leaves gaps.

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 front-loaded sentence with no filler. The negative scope is concise and meaningful, and every word contributes to the tool's selection and invocation.

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?

Given 9 optional parameters, no annotations, and no output schema, a one-sentence description is under-specified. It does not explain the return shape, whether unused parameters are ignored, or how to resolve the mismatch between the narrow 'hostname' purpose and the broad optional schema.

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 coverage is 100%, so the baseline is 3. The description adds hostname-label context, but it does not clarify that 'host' is the relevant parameter among 9 optional fields, nor what the other parameters mean for this tool. It does not materially exceed the schema's own descriptions.

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 the exact operation ('Split'), the target ('a hostname'), and the output ('labels'), and adds a clear negative scope ('without WHOIS or ownership data'). This distinguishes it from sibling shape/lookup tools that operate on URLs, files, repos, or ownership data.

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 clearly scopes use to hostname label splitting and tells the agent what the tool will not provide (WHOIS/ownership). It does not explicitly name sibling alternatives or provide when-not conditions, so it stops short of a 5.

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