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

No annotations are provided, so the description carries the full burden. It mentions 'without WHOIS or ownership data,' which implies a local, non-network operation, but it does not explain side effects, data handling (many fields are 'discarded after the check'), or potential limitations. The description is too thin to establish a clear behavioral contract.

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 sentence, which is concise and front-loaded with the action. However, it is under-specified for a tool with nine parameters, and the structure does not help an agent understand the tool's scope. It is not verbose, but the brevity comes at the cost of completeness.

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 nine parameters, none required, and no output schema. The description only covers hostname splitting, which matches maybe one parameter (host). It is completely inadequate for an agent to understand what to do with url, city, feed, json, path, zone, query, etc. The description gives almost no context for the tool's actual behavior across its parameter set.

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%, with each of the 9 parameters already documented (e.g., 'Git ref name; discarded after the shape check'). The tool description adds no extra meaning beyond the schema, but it doesn't need to because the schema is self-explanatory. The baseline of 3 applies since the schema does the heavy lifting.

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 a limitation (without WHOIS/ownership data), but it is misleading because the input schema accepts nine different kinds of inputs (url, city, feed, json, path, zone, query, etc.) that have nothing to do with hostname splitting. It fails to differentiate from sibling tools like figma-url-shape or github-repo-shape, which likely have similar shape-check purposes. The purpose is too narrow relative to the schema.

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?

There is no guidance on when to use this tool versus the many siblings (normalize-url, figma-url-shape, github-repo-shape, jira-key-shape, etc.). The description gives no context for choosing it, no exclusions, and no alternative suggestions. An agent has to infer from the schema, which is ambiguous.

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