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

No annotations are present, so the description carries the full burden of behavioral disclosure. It does add one useful trait—that no WHOIS/ownership lookup is performed—but says nothing about return format, error behavior, case handling, IDNs, or what happens with the other seven schema parameters. This is a significant gap for a tool with a multi-property schema.

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 a single sentence with no filler, front-loaded with the verb and object. It is appropriately concise, though it could trade some brevity for behavioral detail. It earns its place.

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 appears simple, but the schema lists 8 optional-looking string parameters and no output schema. The description covers only hostname splitting and leaves unanswered which parameters are actually used, whether others are ignored or invalid, and what the returned labels look like. An agent cannot confidently invoke this tool correctly based on the description alone.

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?

The input schema provides descriptions for all 8 properties, so the baseline is 3. The description adds meaning for 'host' by specifying it is split into labels, but it provides no additional context for ref, url, city, feed, json, or path. The net contribution beyond the schema is modest.

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 ('Split') and resource ('a hostname'), and adds scope by excluding WHOIS or ownership data. It distinguishes the tool from enrichment-oriented tools, though it does not reference sibling tools explicitly. This is clear and specific but not perfect.

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 on when to use this tool versus alternatives like normalize-url, fetch-status, or github-repo-shape. The 'without WHOIS or ownership data' clause implies a boundary but provides no explicit conditions or alternative names. An agent is left to infer applicability.

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