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

In the absence of annotations, the description does provide some behavioral context: it states that WHOIS and ownership data are not included and the operation is a pure split. It leaves gaps around whether any network access occurs, how the non-host parameters are treated, and what exact shape the labels result takes, so it is adequate but not rich.

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 one tight sentence with no filler. It front-loads the action and the key limitation, making it very easy for an agent to parse the core purpose quickly.

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 nine optional parameters, no required parameters, no output schema, and no annotations, the single sentence is not enough context. It does not tell the agent which parameter to populate, why the other parameters appear in the schema, or what format the returned labels take.

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 and every parameter already has its own description. The tool description adds no parameter-level meaning and does not explain why eight of the nine accepted properties are unrelated to splitting a hostname.

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 clearly names the operation and resource: 'Split a hostname into labels', and it adds a meaningful non-goal, 'without WHOIS or ownership data', that distinguishes it from lookup and availability tools. It is not a 5 because the nine-parameter schema includes many unrelated fields such as city, json, and query, which the description never reconciles with the hostname-only purpose.

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 when-to-use guidance is given relative to sibling tools such as normalize-url, browser-url-ok, github-repo-shape, or wiki-title-ok. The 'without WHOIS or ownership data' phrase implies a lightweight use case but does not state conditions, alternatives, or exclusions.

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