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 discloses that the tool does not provide WHOIS or ownership data, which is a behavioral limit. However, it does not describe what happens to the 'json' parameter (stated as 'discarded after the check' in the schema), input validation behavior, or any edge cases around hostname format handling.

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 with zero wasted words. It is front-loaded with the primary action ('split a hostname into labels') and immediately follows with the key exclusion ('without WHOIS or ownership data'). No unnecessary elaboration.

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 parameters (all optional), no output schema, and no annotations. The description explains the core purpose but does not clarify why a tool that splits hostnames would accept a 'url', 'json', and 'zone' parameter. Without an output schema or richer behavioral details, an agent may be uncertain about which parameters to supply together and what the return value looks like.

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 schema already documents all four parameters. The description adds the top-level behavioral context that the tool splits hostnames into labels and does not do WHOIS/ownership lookup, which helps the agent understand the tool's intent. While the description does not explain each parameter individually, the schema fully covers this, making the combination solid.

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 'Split a hostname into labels without WHOIS or ownership data' uses a specific verb ('split') and resource ('hostname'), and explicitly states what it does NOT do (no WHOIS or ownership data), which distinguishes it from tools that might fetch domain registration or ownership information. This makes the purpose clear and unambiguous.

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 implicitly suggests this tool is for hostname label splitting rather than WHOIS lookups or ownership queries, but it does not explicitly state when to use this tool versus alternatives. There is no mention of scenarios where it would be more appropriate than sibling tools, nor any exclusions for when not to use it.

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