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

There are no annotations, so the description carries the burden. It does disclose a meaningful behavioral limitation: the tool does not return WHOIS or ownership data. It does not state whether the operation is purely local/read-only, what happens with invalid hostnames, or what the exact return format is, but the 'split into labels' phrasing makes the core behavior reasonably 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, front-loaded sentence with no filler. It states the action, the resource, and an important exclusion without wasting words.

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 annotations, no output schema, nine optional parameters, and zero required parameters, yet the description does not explain which parameter to provide, whether the tool returns an array of strings or some other structure, or how invalid input is handled. The 'hostname' mention and 'host' parameter create a reasonable guess, but the definition is not complete enough for an agent to invoke this tool confidently.

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 and the description does not need to restate parameter details. The description adds no parameter-specific semantics, such as clarifying that 'host' is the relevant field or that the other parameters are ignored. The schema's per-property descriptions provide some meaning, but the tool-level description does not help an agent select among the nine optional parameters.

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 clearly states a specific verb and resource: split a hostname into labels, and it explicitly excludes WHOIS/ownership enrichment. This is enough to distinguish the core action from the broader sibling shape-check tools, though it does not name a specific sibling. The clarity is somewhat reduced by the 9-parameter optional schema, which obscures which input actually represents the hostname.

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 when to use the tool: when you only need the syntactic labels of a hostname and do not want WHOIS or ownership data. However, it gives no explicit alternatives or when-not-to-use guidance, and it does not clarify whether it should be used with a bare hostname versus a full URL despite the schema containing both 'host' and 'url' parameters.

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