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

With no annotations provided, the description carries the full transparency burden. It usefully clarifies that no WHOIS or ownership lookup happens, which prevents an agent from expecting enrichment, but it does not disclose how url, json, or zone inputs affect behavior, whether network calls occur, or any side effects.

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, front-loaded sentence that immediately states the core action and a key exclusion. It is lean and efficient, though the brevity sacrifices behavioral detail. It is genuine specification, not tautology, so it earns a solid score on conciseness.

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 no annotations, no output schema, and four heterogeneous optional parameters, this description is too thin. It never explains how JSON validation and timezone handling fit with 'splitting a hostname,' nor what return shape or error conditions the agent should expect. An agent cannot confidently predict the tool's behavior with non-hostname inputs.

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 is 3. The tool description adds nothing about parameters—it only references 'hostname' and ignores url, json, and zone. No additional formatting, constraints, or relationships are explained, so it neither improves nor harms parameter understanding.

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 and resource: 'Split a hostname into labels.' It also draws a boundary by saying 'without WHOIS or ownership data,' which helps distinguish it from enrichment tools. However, it ignores three of the four schema inputs (url, json, zone), so it does not fully represent what the tool actually accepts.

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?

No explicit when-to-use or when-not-to-use guidance is provided. The phrase 'without WHOIS or ownership data' weakly implies a cheap-labeling use case, but no alternative tools or exclusions are mentioned, and the agent is left to infer relevance from the name and schema.

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