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

With no annotations, the description carries the transparency burden. It discloses a key behavioral trait: the tool will not return WHOIS or ownership data, and describes the operation as a pure split. It does not mention return format, edge cases, or that unrelated parameters are ignored, though some of that is covered by schema descriptions.

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, front-loaded with the core action and followed by the exclusion. Every word earns its place; no redundant or filler content.

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 minimally adequate for a simple shape-checking tool, but incomplete in context: no annotations, no output schema, and no tool-level guidance for how the nine optional parameters relate to the operation. Schema descriptions compensate for individual parameters, but the description doesn't state return format or behavior for malformed hostnames.

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 applies and the schema already documents all nine parameters, including discard behavior. The description adds only the conceptual mapping of 'hostname' to the `host` parameter and contributes no additional parameter-specific semantics.

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?

Clearly states a specific verb ('Split'), a specific resource ('hostname'), and the outcome ('labels'). It also sets a boundary ('without WHOIS or ownership data'), which prevents agents from expecting enrichment. It doesn't name sibling shape tools, but the hostname scope is enough to identify the tool.

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 it: when hostname label splitting is needed, and not when WHOIS or ownership information is required. It does not explicitly name alternative tools or provide a conditional decision rule, so the guidance remains implicit rather than explicit.

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