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

With no annotations, the description carries the behavioral burden. It is usefully transparent that the tool does not provide WHOIS/ownership data, but it does not disclose behavior for invalid hostnames, normalization, multiple inputs, or the exact return shape beyond 'labels.'

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 contributes to stating the action or an important exclusion.

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?

The tool exposes 9 optional parameters and has no output schema, yet the description only explains the hostname-splitting case. It does not explain why ref, url, city, feed, json, path, zone, and query are present or which invocation the agent should use, leaving the definition incomplete.

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 schema already documents every parameter, including which values are discarded. The description adds little parameter-level meaning beyond mapping to the 'host' field.

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 uses a specific verb ('split') and a specific resource ('hostname'), and it states the output is labels. It also scopes out WHOIS/ownership data, but it does not explicitly distinguish this tool from siblings like normalize-url or github-repo-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?

There is no guidance on when to choose domain-shape over the many sibling shape/url/validation tools, and no exclusion conditions are provided. The core action is clear, but the description leaves the selection decision entirely to the agent.

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