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

With no annotations, the description carries the full burden of behavior disclosure. It communicates a pure transformation but fails to mention the tool's broader behavior: the schema shows many unrelated inputs that are 'discarded after the shape check', and there is no indication of return values or side effects.

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 filler and a useful scoping clause. It is appropriately concise, though the extreme brevity contributes to the completeness gap.

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 nine optional parameters, no annotations, no output schema, and a family of sibling shape tools, one sentence about hostname splitting is inadequate. It does not explain the overall purpose, the role of the other parameters, what output to expect, or when it should be preferred.

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 the baseline is 3 even without parameter details in the description. The description adds nothing beyond the schema and creates friction by mentioning only the hostname while the schema exposes eight other parameters, but the schema descriptions themselves are informative.

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') and adds a scope boundary ('without WHOIS or ownership data'). It is clear at a glance, though it does not explicitly differentiate itself from sibling shape-check 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 phrase 'Split a hostname into labels' implies when to reach for it, and 'without WHOIS or ownership data' gives a negative boundary against ownership-lookup use cases. However, it never names alternatives or states explicit conditions for choosing this tool over sibling tools like figma-url-shape or github-repo-shape.

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