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

With no annotations, the description carries the burden of explaining side effects, return values, and limitations, but it only states that it splits a hostname and omits WHOIS/ownership. It does not disclose what output shape is produced, whether network access occurs, or that most input parameters are described in the schema as discarded. This is minimal non-misleading but insufficiently transparent.

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; the core action appears first and the negative scope ('without WHOIS or ownership data') is placed at the end. It earns its place as a terse summary. It loses a point because it is so short that important operational context is omitted, making it concise rather than comprehensive.

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?

Despite the schema describing each parameter at 100% coverage, the tool description itself is incomplete: there are ten optional parameters with no required set, no output schema, and no explanation of what 'labels' looks like in the result. An agent cannot know whether to pass host, url, website, or something else, nor what the return value will be. This is not enough guidance for correct invocation.

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 baseline is 3; the parameter descriptions in the schema are individually clear (e.g., host is 'Public hostname', website includes robots.txt details). The tool description adds no mapping between its hostname-splitting behavior and the ten optional parameters, leaving which parameter to pass ambiguous. A 3 is appropriate because the schema does the heavy lifting.

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 resource ('a hostname into labels'), so an agent can tell this operates on hostnames rather than performing a generic lookup. The qualifier 'without WHOIS or ownership data' adds a clear non-goal. However, it does not distinguish domain-shape from sibling shape tools such as github-repo-shape or normalize-url, so it stops short of a 5.

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 explicit guidance about when to choose domain-shape over its siblings or when not to use it beyond the implied 'no WHOIS/ownership' boundary. The description does not mention any prerequisites, required parameters, or alternative tools for ownership data. An agent is left to infer the intended use case from the name and one-sentence description.

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