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

With no annotations, the description must fully disclose behavior, but it only says 'split a hostname into labels' and what it doesn't do. It does not mention that the tool likely validates multiple input shapes (as implied by schema fields with 'discarded after the check'), nor does it describe return values, error conditions, or side effects. The description is misleadingly narrow.

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 with no wasted words. However, its brevity comes at the cost of necessary detail; it is front-loaded with the core action but omits critical context. It earns a 4 for conciseness but is not ideal because under-specification is not the same as effective conciseness.

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, this description is severely incomplete. It does not explain the purpose of most parameters, does not describe the return format, does not specify when to use it, and fails to clarify the tool's actual behavior. An agent cannot confidently invoke this tool correctly based solely on the description.

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?

While schema coverage is 100%, the description adds no parameter meaning beyond what the schema states. It only references the 'host' concept, but does not explain the relevance of the other 8 parameters. The description's focus on hostname splitting contradicts the schema's broader validation purpose, so it fails to add value and actually confuses parameter semantics.

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 a clear limitation ('without WHOIS or ownership data'), which gives some purpose clarity. However, it does not align with the input schema, which contains 9 parameters including ref, city, json, etc., implying a broader shape-checking purpose. The description also does not distinguish it from the many sibling tools explicitly, and the name 'domain-shape' is vague.

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 on when to use this tool versus alternatives is provided. There is no mention of when it should be preferred over tools like 'normalize-url' or 'github-repo-shape', nor any exclusions. The only hint is the negative statement about WHOIS/ownership, which is a limitation, not a usage directive.

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