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

With no annotations, the description carries the full burden. It discloses that the operation does not include WHOIS/ownership data, which is a behavioral trait. However, it does not state whether this is read-only, what it returns (e.g., array of labels), or how it handles invalid inputs. The one-sentence description gives minimal transparency.

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 with no wasted words. It is front-loaded with the core action and a key exclusion. Efficient and to the point.

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?

With 4 parameters, no output schema, and no annotations, the description is too brief to cover the tool's full behavior. The heterogeneous parameter set (url, host, json, zone) suggests the tool may have multiple modes, yet the description only mentions hostname splitting. Important details like return format, error handling, and parameter usage are missing.

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?

Although schema coverage is 100%, the parameter descriptions are generic and not aligned with the tool's stated purpose. For example, 'json' is described as 'discarded after the check' and 'zone' as 'IANA timezone name', which are unrelated to splitting a hostname. The tool description does not explain how these parameters map to the tool's function, leaving the agent confused about which parameter to use.

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 explicitly excludes WHOIS/ownership data, which distinguishes it from siblings like normalize-url. However, it doesn't clarify how the input parameters (url, host, json, zone) relate to this purpose, so it's clear in intent but slightly ambiguous in scope.

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 alternatives. It does not mention any conditions, prerequisites, or exclusions. The agent must infer from the name and description alone, which is insufficient for choosing among 11 siblings.

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