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

With no annotations, the description carries the full burden of behavioral disclosure. It does add one meaningful constraint: the tool avoids WHOIS/ownership data. Yet it does not state whether the operation is purely local string parsing, how invalid hostnames are handled, or what the output structure is, so behavioral transparency is only partially covered.

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?

A single sentence that is directly informative and front-loaded. The core action comes first, and the restriction 'without WHOIS or ownership data' is a meaningful addition with no filler.

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 description is sufficient for a very simple split operation, and 'into labels' hints at the return shape. However, there is no output schema, no explicit statement that 'host' is the required input, and no guidance on how ignored schema fields should be handled, leaving some room for agent uncertainty.

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 input schema already documents all seven parameters, including 'host' as 'Public hostname', so schema coverage is high. The description adds no extra parameter-level detail and does not explicitly say that 'host' is the relevant field or that the other parameters are ignored for this tool.

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, 'Split', and a concrete resource, 'a hostname', with a clear result: 'labels'. The phrase 'without WHOIS or ownership data' helps distinguish it from lookups, but it does not reference any sibling tool explicitly, so it stops short of full sibling-level differentiation.

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 implies when to use the tool: when only the structural labels of a hostname are needed, not ownership or WHOIS metadata. However, it does not name alternatives (e.g., normalize-url, web-fetch) or state when to prefer those instead, leaving the routing decision to inference.

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