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

With no annotations, the description carries the full behavioral burden. It usefully discloses that the tool does not provide WHOIS or ownership data, which is a meaningful boundary. However, it does not describe the return value format, behavior on invalid input, or how multiple accepted parameters are handled.

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 or repetition. It communicates the core operation and a key non-feature in very few words, making it easy for an agent to parse quickly.

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 a tool with nine optional parameters, no output schema, and no annotations, a one-line description is under-specified. The agent is not told which parameter to pass, what the returned labels look like, or what happens when multiple parameters are provided. The description establishes intent but not enough operational detail for reliable 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 even though the description adds no parameter-specific detail. The description's mention of 'hostname' loosely aligns with the 'host' parameter, but it does not clarify which of the nine optional parameters to populate or whether irrelevant parameters are truly discarded.

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 object: 'Split a hostname into labels.' It clearly identifies the tool's core function and distinguishes it from sibling 'shape' tools like github-repo-shape and jira-key-shape by focusing on hostnames. The phrase 'without WHOIS or ownership data' adds useful scope, though it doesn't specify which input parameter should be used.

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 use this tool versus alternatives. The only hint is 'without WHOIS or ownership data,' which implies a limitation but does not name a preferred alternative or provide a decision rule. An agent would have to infer usage context from the tool name and sibling set.

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