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

With no annotations, the description must carry safety/behavior information; the phrase 'without WHOIS or ownership data' partially does this by indicating a pure parsing operation rather than a lookup. It does not explicitly state read-only behavior, side effects, or return format, but for a string-splitting operation the implied behavior is reasonably clear.

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. Every word contributes the core action or a scope limitation.

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 such a short operation the description is mostly adequate, but the schema lists nine unrelated optional parameters and there is no output schema, so an agent is left to infer what 'labels' returns and which parameter is the intended input. The parameter descriptions mitigate this, but the tool description itself is thin.

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%: all nine optional parameters have individual descriptions, so the baseline is 3 and the description need not repeat them. The description's 'hostname' language loosely aligns with the 'host' parameter, but it does not explicitly tell the agent which of the nine optional parameters to supply.

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 and resource: 'Split a hostname into labels', and adds a negative scope ('without WHOIS or ownership data') that sets expectations. This clearly differentiates it from sibling shape tools like github-repo-shape or jira-key-shape.

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 a clear use case (split hostnames) and an exclusion (no WHOIS/ownership data), so an agent knows not to call it for ownership lookups. However, it does not name alternative tools or specify when to prefer this over the many sibling shape/url tools.

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