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

With no annotations, the description carries the full burden, and it is thin: it says what the tool does not do (WHOIS/ownership) but not behavioral details such as whether it performs DNS lookups, normalizes casing/IDN, handles IP addresses, or what errors occur for invalid hostnames. The negative scope is useful, but the positive behavior is under-specified.

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 focused sentence and earns credit for being short and front-loaded with the core action. But it is unexpectedly terse given the presence of four heterogeneous parameters, so it reads more like an under-specification than a deliberate minimalism.

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 unrelated parameters, no annotations, and no output schema, this description is incomplete. It does not explain how parameters map to the splitting behavior, whether inputs are mutually exclusive, or what the return value contains — leaving an agent to guess essential invocation details.

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 already has a description. However, the description's 'Split a hostname' does not clarify how the four parameters — url, host, json, zone — relate to that action, leaving ambiguity about which is required or how they interact. It adds no meaning beyond the schema, so the dimension earns the baseline 3.

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 uses a specific verb ('Split') and resource ('a hostname into labels'), and adds an exclusion ('without WHOIS or ownership data') that helps distinguish it from domain intelligence tools. It does not explicitly name a sibling, but the scope is clear enough to separate it from typical URL/WHOIS utilities.

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 gives no direct guidance on when to choose this tool over alternatives. It implies a narrow parsing purpose, but there are no stated conditions, examples, or references to sibling tools that would help an agent decide between this and other domain-related tools.

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