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

With no annotations, the description carries the full burden. It does say 'without WHOIS or ownership data', implying a local, side-effect-free operation, but it does not describe output format, error behavior, or edge cases. For a simple parser this is minimally adequate, not comprehensive.

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 concise sentence that is front-loaded with the core action. It omits necessary contextual detail but does not waste words, so it earns a solid score for conciseness despite being under-specified.

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?

Given 4 parameters, no annotations, and no output schema, the description is too thin. It does not say what the output looks like, which 'labels' means, or that parameters like 'json' and 'zone' are irrelevant to the core function. An agent cannot reliably invoke this tool correctly from 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?

Schemas cover 100% of parameter descriptions, but the tool description ('split hostname') does not align with the actual parameters (url, host, json, zone). It never explains which parameter to use for the hostname, and 'json' and 'zone' seem unrelated to hostname splitting. The description adds more confusion than semantic value.

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 action ('split a hostname into labels') and a resource ('hostname'), and clarifies that it excludes WHOIS or ownership data. This distinguishes it from tools that might enrich domains with registry data, though it doesn't explicitly contrast with siblings.

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?

The description gives no indication of when to use this tool versus sibling tools like 'normalize-url' or 'inspect-robots'. There are no conditions, exclusions, or alternatives mentioned, so an agent must infer usage solely from the action phrase.

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