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

There are no annotations, so the description carries the behavioral disclosure burden. It adds a meaningful limitation ('without WHOIS or ownership data') and implies a pure lexical operation, but it does not describe return value shape, edge-case handling, or whether the operation is read-only.

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. Every word earns its place: the operation, the target resource, and the key exclusion are all included efficiently.

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, this terse description leaves too much unspecified. An agent cannot be sure whether to pass only 'host', whether other fields are ignored, or what the split result looks like (array, delimited string, case handling, etc.).

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 description coverage is 100%, so the baseline is 3. Each parameter already has explanatory text, including 'discarded' notes for several fields. The description adds some value by implying the 'host' field is the relevant one, but it does not explicitly say which of the 9 optional parameters should be populated.

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.' The qualifier 'without WHOIS or ownership data' distinguishes this tool from richer domain-lookup tools and clarifies its scope relative to shape-check siblings like github-repo-shape and jira-key-shape.

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 clear context is that this tool is for hostname label splitting, not for WHOIS or ownership lookups. However, it does not explicitly name alternative tools or state when-not-to-use conditions beyond the 'without WHOIS or ownership data' caveat.

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