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

With no annotations, the description must carry the behavioral burden. It discloses that the tool does not fetch WHOIS/ownership data, which is a useful trait. However, it does not mention error handling, return format, or whether the operation is local or network-based. The disclosure is minimal but not misleading.

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, efficient sentence with no fluff. It front-loads the core action and includes a relevant exclusion. Every word earns its place.

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?

Despite a simple purpose, the tool has 9 parameters, no output schema, and no annotations. The description fails to specify which parameter to use for the hostname or what the output looks like. An agent would struggle to call this tool correctly without inspecting the schema and inferring the relevant parameter. The description is too thin for the given complexity.

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 has 100% description coverage, so each parameter is documented. The description does not add any parameter-level detail, nor does it indicate which parameter (likely 'host') is the primary input. Given high schema coverage, the baseline is 3, and the description does not raise it.

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'. It also clarifies a key exclusion ('without WHOIS or ownership data'), which differentiates it from ownership-related sibling tools. This is not a tautology and clearly conveys what the tool does.

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 a lightweight shape operation by excluding WHOIS/ownership data, but it does not explicitly state when to use this tool over alternatives or name any sibling tools. There is no clear 'use this when...' guidance, only an implicit context. The exclusion is useful but not sufficient for routing decisions.

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