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 only states that the tool splits a hostname and omits WHOIS/ownership data—it says nothing about side effects, return values, rate limits, or operational constraints. Given the schema hints that many inputs are 'discarded after the call,' the description fails to explain this behavior, leaving the agent with minimal insight.

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, which is structurally efficient. However, it is so brief that it omits critical information about the tool's multi-parameter nature and alternatives. It is concise but at the expense of completeness—concision without substance does not earn a higher 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?

For a tool with 9 parameters, no annotations, and no output schema, the description is grossly inadequate. It covers only one facet (hostname splitting) and leaves the purpose of all other parameters unexplained. There is no mention of return format, error behavior, or use cases. The description fails to provide the essential context an agent needs to call this tool correctly.

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% and each parameter has its own description, so the schema already documents parameter meaning. However, the tool description only addresses 'hostname' and gives no unifying explanation for the other eight parameters. An agent would not infer that the tool can handle URLs, cities, JSON, etc., nor how these relate to 'domain-shape.' The description adds little semantic value beyond the schema and even hinders understanding of the parameter set.

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 notes a limitation (no WHOIS/ownership data), which helps distinguish it from data-enrichment tools. However, it misrepresents the tool's scope: the input schema accepts nine different parameter types (ref, url, city, feed, json, path, zone, query) each with its own purpose, yet the description only mentions hostname. This creates confusion about what the tool actually does and which input to use.

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 its many siblings (normalize-url, playwright-url-ok, fetch-status, etc.). The description does not state prerequisites, exclusions, or alternative tools. The single sentence implies hostname-only usage, which directly conflicts with the schema's broader input set, providing misleading usage clues.

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