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

With no annotations, the description must carry the behavioral burden. It discloses that the tool operates 'without WHOIS or ownership data', which is a useful constraint, but it omits critical details such as whether the operation is read-only, what the output format is, and how the json and zone parameters interact with the described behavior. The schema description for json says 'JSON text to validate; discarded after the check', implying a validation behavior not mentioned in the description, creating inconsistency.

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 sentence, so it is concise and free of fluff. However, it is so terse that it fails to provide any structure or context beyond a minimal statement. It does not front-load key information like usage or parameters, making it merely a label rather than a useful guide.

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 4 optional parameters and no output schema, the description is severely incomplete. It does not explain how to construct a valid call, what the expected inputs are, or what the tool returns. The presence of parameters like 'json' and 'zone' that seem unrelated to 'splitting a hostname' adds confusion. An agent cannot reliably invoke this tool correctly based on the provided 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?

Schema description coverage is 100% (each parameter has a description), so the baseline is 3. The tool description adds no additional meaning about parameters, but since the schema already documents each parameter adequately, the description does not need to repeat them. However, the description does not clarify how parameters relate to the tool's core purpose, which might be expected.

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'. However, it is ambiguous how this relates to the four parameters (url, host, json, zone) which suggest a broader scope. It does not clearly differentiate from sibling tools like normalize-url or validate-json, which are likely to have overlapping functionality.

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 alternatives. The description does not mention any conditions, exclusions, or comparisons to sibling tools. An agent has no basis to decide whether to call domain-shape or a different tool.

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