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

With no annotations, the description carries the burden of explaining behavior. It discloses the non-lookup behavior (no WHOIS/ownership), which is useful, but it does not mention output format, invalid-host handling, or the fact that only the 'host' parameter is relevant among the many schema fields.

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 front-loaded sentence with no filler. The qualifier about WHOIS/ownership earns its place by setting the tool's boundary.

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 simple parser the description communicates the main behavior, but with no output schema and a schema full of apparently unrelated fields, an agent would benefit from knowing the exact return shape and that only 'host' is consumed.

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 high: every parameter, including 'host', has a description, so the description adds only the 'labels' detail and the WHOIS exclusion. That is reasonable but does not go 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 uses a specific verb and resource — 'Split a hostname into labels' — and adds a clear boundary with 'without WHOIS or ownership data'. This distinguishes domain-shape from sibling shape/URL tools that may resolve or enrich hostnames.

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?

It states the tool's context: use it for syntactic hostname splitting. The phrase 'without WHOIS or ownership data' excludes ownership/resolution use cases, though no sibling tool is named as an explicit alternative.

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