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

With no annotations, the description carries the burden and it does add a behavioral boundary: it will not return WHOIS or ownership information. However, it does not state what the returned labels look like, edge-case behavior, or that most schema parameters are discarded after the shape check.

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 states the core behavior and the key limitation with no filler. It is concise without sacrificing the most important distinguishing information.

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 nine parameters, no annotations, and no output schema, this description is too thin to fully support correct invocation. The agent cannot tell which parameter to populate or what the splitter returns, especially given the unrelated-looking schema fields.

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 reinforces the hostname intent but does not explain why the schema exposes unrelated parameters such as city, feed, json, and query, nor how they relate to the stated domain-splitting behavior.

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 gives a specific operation — 'Split a hostname into labels' — with a clear resource, and the 'without WHOIS or ownership data' clause sets it apart from enrichment-style domain tools. It is not a 5 because the description ignores the nine-parameter schema, so the exact scope of the tool is still ambiguous.

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?

No guidance is provided for when to prefer this tool over siblings such as github-repo-shape, normalize-url, or browser-url-ok. The only hint is a negative one ('without WHOIS or ownership data'), which does not state a use condition or alternative.

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