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

With no annotations provided, the description must carry the full behavioral burden. It only says 'without WHOIS or ownership data', which hints at one constraint, but fails to disclose the 'shape check' behavior hinted by the parameter descriptions ('discarded after the shape check'). The inconsistency between 'split' and 'shape check' leaves behavior opaque.

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, front-loaded sentence with no fluff, but it is so terse that it omits essential information. Conciseness is achieved at the expense of clarity, which is a trade-off that warrants a mid-range score.

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 9 optional parameters, no required fields, no output schema, and no annotations, the description is severely incomplete. It fails to explain what the tool returns, how the parameters are used, or how the 'shape check' works. An agent cannot confidently call this tool based on the provided information.

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 coverage is 100%, so each parameter has a description, but the tool description does not explain how any of these parameters relate to splitting a hostname. The mention of 'discarded after the shape check' in the schema is the only hint, yet the tool description never ties the parameters to its stated purpose, adding no semantic value beyond the schema.

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 it contradicts the breadth of the input schema, which accepts city, feed, json, path, zone, query, and more. The stated purpose does not match the tool's actual parameter surface, making it confusing for an agent to discern what the tool actually does.

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 mention of when to use this tool versus siblings like 'url-ok', 'geo-hint', or 'validate-json'. There is no guidance on prerequisites, exclusions, or alternative selection, leaving the agent to guess which tool fits a given task.

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