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

With no annotations present, the description carries the burden. It usefully discloses that the tool performs no WHOIS/ownership lookup, but it does not clarify output structure, error behavior, or that all inputs are ephemeral/discarded. The schema descriptions add discard details, but the tool description itself gives only a thin behavioral picture.

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 with no filler. It states the core operation and the key limitation without wasting words.

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?

Despite having eight parameters and no output schema, the description only explains hostname splitting. It fails to explain how the other schema fields relate to the tool, what the return value looks like, or how this tool differs from the many sibling tools with similar URL/hostname purposes.

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 eight parameters with descriptions, including what is discarded, so schema coverage is high and the baseline is 3. The tool description adds no extra parameter-level meaning, but it also does not need to because the schema carries that weight.

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'), a concrete resource ('hostname'), and a clear scope (labels only, no WHOIS/ownership data). It differentiates the tool from ownership/enrichment lookups, though it does not explicitly contrast with sibling tools like normalize-url or web-fetch.

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 'without WHOIS or ownership data' clause implies this is a syntactic-only tool, so an agent can infer not to use it for enrichment. However, there is no explicit guidance about when to pick this over sibling URL/hostname tools, nor any exclusions or alternative conditions.

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