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

With no annotations, the description carries full behavioral burden, but it only reports a parse action and excludes WHOIS/ownership data. It does not disclose that inputs are discarded after checks, what happens for invalid input, or whether any side effects occur; the schema-level 'discarded' notes are not part of the tool description.

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 with no filler. The action is front-loaded, and the limiting clause 'without WHOIS or ownership data' earns its place by setting expectations about scope.

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 optional parameters and no output schema, the definition is incomplete. It explains only the hostname case, gives no return-shape information, and leaves the purpose of the other eight accepted inputs unexplained in the description. The schema descriptions rescue parameter semantics but not overall tool behavior.

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; the description does not need to explain every parameter. It adds no meaning beyond identifying host as the hostname, leaving the mapping of ref, city, feed, json, path, zone, and query to the schema descriptions alone.

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 boundary ('without WHOIS or ownership data'), so the core purpose is recognizable. However, it only describes one of the nine schema inputs and does not reflect the broader shape-check behavior hinted at by params like ref, json, path, and query.

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 explicit guidance on when to use this tool versus sibling tools such as normalize-url, fetch-status, or validate-json. The negative clause 'without WHOIS or ownership data' is the only hint, but it names no alternatives or selection conditions.

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