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

With no annotations provided, the description must disclose behavior but only mentions 'without WHOIS or ownership data'—a single, narrow detail. It does not explain what the tool actually does with the other parameters, what it returns, or any side effects. The description's claim to split hostnames contradicts the broad set of inputs in the schema, leaving agent behavior unclear.

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 concise sentence with no unnecessary words. However, it is under-specified relative to the tool's complexity (9 parameters) and does not front-load the broad capability. Conciseness is acceptable, but structure fails to cover the tool's actual functionality.

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?

For a tool with 9 parameters, no output schema, and no annotations, the description is grossly incomplete. It addresses only one parameter (host) and ignores the rest, providing no rationale for the other inputs or the tool's overall purpose. An agent cannot determine correct usage for any input other than host.

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 schema descriptions cover 100% of the parameters, so the baseline is 3. The description does not add meaning beyond the schema for any parameter—it only repeats the concept of hostname for 'host' and provides no explanation of how the other parameters relate to the tool's purpose. This meets the baseline but adds no value.

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') but the schema accepts 9 different input types (ref, url, city, feed, host, json, path, zone, query), none of which are mentioned beyond host. This creates confusion about the tool's actual scope—it appears to be a generic shape-checker rather than a hostname splitter, making the purpose misleading.

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 given on when to use this tool versus sibling tools like normalize-url, browser-url-ok, or file-path-ok. The description does not provide any context about the tool's role in a workflow or scenarios where it should be preferred.

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