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

No annotations exist, so the description alone must carry the burden of behavioral disclosure, and it only contributes the negative constraint 'without WHOIS or ownership data.' It does not state that inputs are discarded after checks, that no parameters are required, whether any network/DNS access occurs, or what the return value is. The schema's per-parameter notes ('discarded after the shape check', 'no disk access') hint at discard semantics, but the tool-level description stays silent on these traits.

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 front-loaded sentence with no filler: 'Split a hostname into labels without WHOIS or ownership data.' Every word earns its place. However, for a tool with nine parameters, no annotations, and no output schema, the brevity edges toward under-specification rather than disciplined conciseness, which keeps it from a 5.

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 is complex — nine optional parameters, no output schema, and a large sibling family — so the description carries a heavy completeness burden and falls short. It does not say which parameter to populate, what happens to the other eight inputs, what the tool returns, or when it is preferable to the -shape/-ok siblings. Only the schema's parameter notes partially compensate.

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% — every one of the nine parameters has its own description — so the baseline is 3. The tool description adds no parameter-level meaning and aligns only with the 'host' parameter ('Public hostname'), leaving the semantics of the other eight parameters entirely to the 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 names a specific verb and resource — 'Split a hostname into labels' — and adds a scope qualifier, 'without WHOIS or ownership data.' However, the schema exposes nine unrelated accepted inputs (ref, url, city, feed, json, path, zone, query) that are all described as discarded, so the description covers only a fraction of the tool's actual surface and does not help an agent tell it apart from the -shape/-ok sibling family. The core statement is clear, but the description-schema mismatch is significant.

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 statement of when to call this tool instead of the many similar siblings (figma-url-shape, github-repo-shape, jira-key-shape, file-path-ok, wiki-title-ok, browser-url-ok). The phrase 'without WHOIS or ownership data' weakly implies a purely syntactic use case, but no explicit conditions, exclusions, or alternative tool names are provided. An agent gets essentially no guidance for tool selection.

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