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

With no annotations, the description carries the full burden of explaining behavior. It discloses one useful limitation (no WHOIS/ownership data), but it does not state whether the operation is read-only, how url/json/zone inputs are handled, or what the output looks like. This leaves the agent uncertain about actual behavior beyond the simple split.

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, economical sentence with no filler; the core operation appears immediately. It is concise, though the brevity comes at the cost of not addressing the other three parameters.

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 four heterogeneous parameters, no annotations, and no output schema, a one-sentence description is insufficient. The description does not say which parameter is the primary input, whether a url is also accepted for hostname extraction, what happens to json and zone inputs, or what result the agent should expect.

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 input schema already documents all four parameters clearly. The description adds no new meaning beyond the word 'hostname', which aligns with the host parameter; it does not clarify how url, json, or zone relate to the 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 states a specific verb ('split') and resource ('hostname into labels'), and adds a meaningful exclusion ('without WHOIS or ownership data') that separates it from domain-enrichment tools. However, it does not explain why the schema also contains url, json, and zone parameters, so the stated purpose only partially covers the tool's apparent input surface.

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 given about when to use this tool versus siblings like normalize-url or validate-json. The phrase 'without WHOIS or ownership data' says what the tool does not return, but it does not indicate which parameter to supply or when this tool is the right choice.

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