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

With no annotations provided, the description must carry the full burden of behavioral disclosure. It only mentions that WHOIS/ownership data is not included, but it does not describe return format, error handling, behavior with invalid or non-hostname inputs, or what happens when multiple parameters are supplied. The tool's behavior with url, json, and zone is entirely unexplained, leaving significant behavioral opacity.

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 concise sentence that front-loads the core action. It is appropriately brief and avoids verbosity. However, it is so minimal that it sacrifices explanatory value, but from a pure conciseness standpoint it is efficient.

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 four optional parameters and no output schema, the description is severely incomplete. It does not explain the purpose of the non-hostname parameters, how the tool chooses which input to process, or what the output looks like. An agent would have to guess which parameter to pass and what to expect in return, making the description insufficient 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?

The schema description coverage is 100%, so the baseline is 3. The description adds no parameter-specific meaning beyond the schema, nor does it explain why url, json, or zone are relevant to splitting a hostname into labels. Since the schema already documents each parameter, the description does not need to repeat that, but it also does not add value on parameter usage or format.

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 verb and resource ('Split a hostname into labels') and adds a differentiator ('without WHOIS or ownership data'), which helps distinguish it from some siblings. However, it fails to clarify how the four input parameters (url, host, json, zone) relate to this core function, leaving ambiguity about what inputs are actually accepted for the splitting operation.

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 provides no guidance on when to use this tool versus the ten siblings. There is no mention of alternatives, exclusions, or context that would help an agent decide between domain-shape and normalize-url, inspect-robots, or iana-zones. The only hint is the 'without WHOIS' phrase, but it does not explicitly state a preferred use case or comparison.

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