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

No annotations are present, so the full burden falls on the description. It discloses the absence of WHOIS/ownership data, but does not say whether any network or side effects occur, what the output looks like, or how errors are handled. The schema's 'discarded' notes hint at statelessness, but the description itself provides little behavioral transparency.

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, front-loaded sentence with no filler. It states the core action immediately and includes a compact qualifier that adds useful scope.

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 definition is incomplete for a tool with seven input parameters and no output schema. It names only hostname behavior and never reconciles the other six schema properties with the stated purpose, nor does it describe return format or failure behavior. The schema's discard notes partially compensate, but the description itself leaves significant gaps.

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 schema already provides good descriptions for all parameters, including which ones are discarded, so the baseline is a 3. The description maps the concept 'hostname' to the tool's purpose but does not clarify why the schema contains ref, url, city, feed, json, and path, nor does it add meaningful parameter-level detail beyond 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 uses a specific verb ('split') and clearly names the resource ('hostname') and outcome ('labels'). It also draws a boundary by stating it does not provide WHOIS or ownership data. It doesn't explicitly distinguish from sibling tools, but the hostname focus is enough to be serviceable.

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 guidance on when to use this tool versus alternatives like normalize-url, github-repo-shape, or web-fetch. The 'without WHOIS or ownership data' phrase implies a boundary, but it does not state when to choose this tool or when to avoid it.

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