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

There are no annotations, so the description carries the behavioral burden. It does state the main transformation behavior and explicitly excludes WHOIS/ownership enrichment, which is helpful. However, it does not disclose return format, network access, side effects, or error behavior.

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?

A single, front-loaded sentence with no filler or repetition. It states the action and the key limitation in a compact, scannable way.

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 output schema, and no annotations, a one-sentence description is not enough for reliable invocation. The description does not say which parameter to supply, what the returned labels look like, or whether the other schema fields are actually used by this tool. This leaves significant ambiguity for an agent.

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 schema already documents each parameter. The description adds general context about hostnames but does not explain how the eight other parameters (ref, url, city, feed, json, path, zone, query) relate to the described split-hostname behavior. Baseline 3 is appropriate because the schema handles parameter semantics, but the description does not help reconcile its narrow purpose with the broad schema.

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 and resource: 'Split a hostname into labels', which clearly conveys the core operation. It also draws a boundary by saying 'without WHOIS or ownership data', helping distinguish it from enrichment-style tools. However, it does not explicitly differentiate from nearby sibling tools like normalize-url or file-path-ok.

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 use case is implied: an agent should use this tool when it needs to split a hostname into labels. The phrase 'without WHOIS or ownership data' hints at when not to use it, but no alternative tools or explicit when-to-use conditions are mentioned. Given the large sibling list, this is a noticeable gap.

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