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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It does disclose one important trait: 'without WHOIS or ownership data,' indicating a limitation. However, it does not mention side effects, persistence, or return behavior. For a simple pure-function tool this is a modest but acceptable disclosure.

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 filler. The primary operation is front-loaded, and the clarifying qualifier 'without WHOIS or ownership data' adds value without bloat.

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 accepts eight heterogeneous parameters (ref, url, city, feed, host, json, path), but the description only mentions splitting a hostname. It does not explain the role of the other parameters or how they are used or discarded. This mismatch leaves the agent without enough context to confidently use the tool when non-hostname inputs are provided.

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 description adds no parameter-specific information, but the input schema provides descriptions for all eight parameters. Since schema coverage is effectively 100%, the baseline of 3 applies. The description's mention of 'hostname' relates to the 'host' parameter, but it does not clarify how other parameters such as 'city' or 'json' relate to the tool's purpose.

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 clearly states the verb and resource: 'Split a hostname into labels.' It also adds a distinguishing qualifier, 'without WHOIS or ownership data,' which clarifies it is not a whois/lookup tool. While it does not explicitly name sibling tools, the scope is specific enough to avoid confusion with URL normalization or other shape-checking 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 provides no guidance on when to use this tool versus alternatives. It simply states what it does; there is no mention of alternative tools like normalize-url or fetch-status, nor any conditions or exclusions. An agent is left to infer usage from the 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.