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

Because no annotations are provided, the description carries the full behavioral disclosure burden. It does communicate a useful behavioral trait: no WHOIS or ownership lookup is performed. However, it does not explicitly state whether the operation is read-only, whether network access occurs, or what the output format is beyond 'labels.'

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 sentence with a front-loaded verb and no unnecessary words. It states the core operation and a key limitation without repetition, 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?

The definition is incomplete for confident invocation: the schema has nine optional parameters and no required fields, but the description does not specify which parameter to populate or that the others are irrelevant. There is no output schema, and the expected return value is only vaguely implied by 'labels.' The schema hints at broader shape-checking behavior, but the description does not reconcile that with its narrow hostname-splitting claim.

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 description only loosely connects 'hostname' to the 'host' parameter and does not explicitly resolve which of the nine optional parameters should be used or that the others are ignored. It adds minimal meaning 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 states a clear, specific operation: 'Split a hostname into labels.' It also adds a distinguishing qualifier, 'without WHOIS or ownership data,' which separates it from ownership-related tools and other sibling shape tools. This is unambiguous and actionable.

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 implies the usage: call this tool when you need to split a hostname into labels. However, it does not explicitly state when not to use it, nor does it name alternatives like github-repo-shape or jira-key-shape. The 'without WHOIS or ownership data' phrase is an implicit exclusion, not a clear usage guideline.

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