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

With no annotations provided, the description carries the full burden. It does disclose that WHOIS/ownership data is excluded, which is a useful behavioral constraint, but it says nothing about return format, error behavior, network activity, or how the json/zone/url parameters behave. The 'discarded after the check' behavior appears only in the schema, not in the description.

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 single sentence is concise, front-loads the core action, and contains no filler. It is too terse for the tool's four-parameter, multi-behavior surface, but as a simple statement 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?

The tool has 4 optional parameters, no output schema, and no annotations, yet the description only covers hostname splitting. It omits return values, valid parameter combinations, and how the url/json/zone parameters relate to the tool's behavior, leaving an agent with significant ambiguity about 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?

Schema description coverage is 100%, so the baseline is 3 and the schema already documents each parameter. The description itself adds no parameter-level guidance, and the mismatch between the 'split hostname' purpose and the unrelated json/zone parameters creates ambiguity about which parameter should be used for which operation.

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 names a specific verb and resource: 'Split a hostname into labels' and adds a clear negative scope, 'without WHOIS or ownership data.' However, it does not mention the URL normalization, JSON validation, or timezone operations suggested by the input schema, so it only partially represents the tool's surface.

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?

No explicit when-to-use guidance or alternative tools are named. The phrase 'without WHOIS or ownership data' implies the tool is not for ownership lookups, but the agent gets no direction on when to choose this tool over siblings or which parameter combinations to use.

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