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

With no annotations provided, the description carries the full burden of behavioral disclosure. It does disclose that no WHOIS or ownership data is included, which is helpful, but it does not describe return format, error handling, or the fact that many schema parameters are 'discarded after the shape check.' This leaves significant behavioral ambiguity for an agent.

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 wasted words. It states the core action and the key exclusion ('without WHOIS or ownership data') efficiently.

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 the tool having nine optional parameters and no output schema, the description gives no details about expected output structure, input constraints, or behavior for invalid hostnames. It also does not explain the schema's 'discarded' semantics, leaving an agent without enough context to invoke the tool confidently in edge cases.

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 schema already documents all nine parameters, including that most are discarded after checks. The description adds a 'hostname' to 'labels' mapping that aligns with the host parameter, but it does not clarify the role of the other optional parameters. Baseline 3 is appropriate given the high schema coverage.

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.' It also adds a clear negative scope, 'without WHOIS or ownership data,' which distinguishes it from lookup or ownership-oriented sibling tools. This is enough for an agent to tell domain-shape apart from URL normalization, fetching, and other shape-check tools.

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 need hostname label splitting and explicitly do not want WHOIS or ownership data. However, it does not name alternatives or state when-not-to-use it relative to sibling tools like normalize-url, file-path-ok, or figma-url-shape, so the guidance is implied rather than explicit.

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