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

With no annotations provided, the description carries the behavioral burden. It discloses that the operation is purely syntactic ('without WHOIS or ownership data'), but it does not mention input handling, errors, or return behavior; schema-level 'discarded' notes do some of this work.

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. It conveys the core operation and a key limitation in minimal 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 description is enough to understand the high-level function, but with no output schema and no indication of which of the nine optional parameters is relevant, an agent is left to infer invocation details. The schema's host description partially compensates.

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. The description adds no parameter-specific meaning; the relevant host parameter is documented only in the schema, and the description does not explicitly map 'hostname' to the 'host' field.

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?

Description states a specific action ('split a hostname into labels') and explicitly excludes WHOIS/ownership enrichment. This clearly distinguishes domain-shape from sibling URL/validation tools like normalize-url, github-repo-shape, and fetch-status.

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 the agent needs hostname labels without ownership data. However, it does not name any alternative tools or give explicit when-not-to-use guidance, leaving routing to inference.

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