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

With no annotations, the description carries the full burden of behavioral disclosure. It discloses one limitation (no WHOIS/ownership data) but omits critical behavior: what the tool returns, how the input parameters are processed, whether any data is discarded (hinted at by some parameter descriptions but not in the tool description), and any side effects. For a tool with 9 parameters, this is a significant transparency gap.

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 wasted words. It front-loads the core action and the key limitation. However, it is perhaps too terse to be fully useful; still, for conciseness and structure, it scores well.

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?

Given 9 parameters, no output schema, and no annotations, the description is insufficiently complete. It fails to indicate which parameter is the primary input (hostname), how other parameters are used, or what the expected output is. An agent would struggle to correctly invoke this tool based solely on the description. The schema covers parameters, but the overall tool behavior remains underspecified.

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 each parameter is documented in the schema. The tool description adds no parameter-level meaning beyond the schema. Per the rubric, with full coverage the baseline is 3, and since the description does not supplement or clarify the parameters (e.g., which one is the hostname), it stays at 3.

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 action ('split a hostname into labels') and includes a distinguishing caveat ('without WHOIS or ownership data'). It is clear enough to differentiate from generic URL tools, though it could more explicitly contrast with sibling shape tools like normalize-url or github-repo-shape. The verb and resource are specific, earning a 4 rather than 5 due to slight ambiguity between 'domain' and '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?

No guidance is provided on when to use this tool versus the many sibling shape/check tools (e.g., figma-url-shape, jira-key-shape, normalize-url). The description gives no context for selecting it, no prerequisites, and no exclusions. The agent must infer usage from the tool name and description alone.

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