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

With no annotations provided, the description carries the full burden of behavioral disclosure. It does state that the tool operates without WHOIS/ownership data, which is a useful constraint, but it fails to disclose that most inputs are discarded after a shape check (as implied by the schema descriptions), that the tool appears to validate multiple input types, or what it returns. For a tool with no annotation coverage, this is a significant gap.

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 no wasted words, so it is concise. However, it is under-specified: it omits essential context about the tool's multi-parameter nature and behavioral constraints. Conciseness is appropriate in length but not in completeness; it does not 'earn its place' because it leaves the agent with more questions than answers.

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?

This is a 9-parameter tool with no annotations and no output schema, yet the description covers only one narrow aspect (hostname splitting). It does not explain the purpose of the other eight parameters, the tool's return value, side effects, or when to use it relative to the many sibling tools. For such a complex and ambiguous tool, the description is grossly inadequate.

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 does not add meaning for the eight non-host parameters; it only implicitly suggests that the 'host' field is the intended input for hostname splitting. It does not clarify which parameter to use for other intended inputs or how the parameters interact. Since the schema already documents each parameter, the description adds minimal value, but it does provide a hint about the primary use case.

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 clear resource, but it fails to reconcile with the input schema, which accepts nine different parameter types (ref, url, city, feed, json, path, zone, query). This mismatch makes the tool's actual purpose ambiguous: it appears to be a general 'shape check' tool rather than purely a hostname splitter. The description is not a tautology but is misleading about scope.

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 phrase 'without WHOIS or ownership data' implies a distinction from ownership-returning tools, but it does not explicitly state when to use this tool versus alternatives. There are many sibling shape tools (e.g., github-repo-shape, jira-key-shape) and the description does not explain when domain-shape is the right choice or when to avoid it. No alternatives are named, and the broader use case for the non-hostname parameters is left entirely unexplained.

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