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

No annotations are provided, so the description carries the full burden. It discloses that the tool operates 'without WHOIS or ownership data', which implies a read-only parsing behavior, but it does not state whether the tool has side effects, what it returns, or how it handles multiple parameters. The description is silent on behavior beyond the single operation.

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, compact sentence that is easy to parse, but it is under-specified for a tool with four parameters. It is concise without being informative, sacrificing necessary detail for brevity.

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?

Given the tool has four optional parameters, no annotations, and no output schema, the description is severely incomplete. It does not explain the purpose of the url, json, and zone parameters, does not describe return values, and gives no guidance on edge cases or parameter interactions. An agent cannot safely call this tool based on the description alone.

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 coverage is 100%, so each parameter has a description, but the tool description adds nothing about them and actually creates confusion. The description only mentions hostname splitting, while the schema accepts url, json, and zone, which seem unrelated. This disconnect means the description fails to add meaningful context 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 specific verb ('Split') and resource ('hostname into labels'), which is clear and distinguishes it from siblings like normalize-url or validate-json that perform different operations. However, it ignores the other three parameters (url, json, zone) which the schema accepts, so the purpose is only partially conveyed.

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?

There is no guidance on when to use this tool versus alternatives. No mention of conditions, prerequisites, or exclusions. An agent cannot tell whether this should be used for URL normalization, JSON validation, or timezone handling given the broad schema, and no sibling references are provided.

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