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

With no annotations provided, the description carries the full behavioral burden. It discloses the core behavior and one limitation (no WHOIS/ownership), but does not mention return format, error behavior, or how the many optional inputs are handled. This is acceptable for a simple read-style operation but not richly transparent.

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. It front-loads the key action and then adds the meaningful scope limitation. Every word contributes to the agent's understanding.

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 9 optional parameters, no required parameters, no output schema, and no annotations, yet the description does not explain which parameter to use, what the return value looks like, or how the unrelated optional inputs should be interpreted. The presence of many 'discarded' schema parameters makes this ambiguity more significant.

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 covers 100% of the parameters with descriptions, so the baseline is 3. The tool description itself adds no parameter-specific meaning beyond the schema, and the hostname wording only loosely maps to the 'host' parameter. The schema does the necessary work here.

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 adds a scoping constraint, 'without WHOIS or ownership data', which distinguishes this from domain/ownership-related sibling tools. An agent can understand exactly what operation this tool performs.

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?

There is no explicit when-to-use or when-not-to-use guidance and no named alternatives. The phrase 'without WHOIS or ownership data' weakly implies that this is for structural hostname splitting only, so usage context is implied rather than stated.

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