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

No annotations are provided, so the description must fully disclose behavior. It reveals the core pure transformation but says nothing about side effects, permissions, return values, or edge cases. The schema's json parameter note ('discarded after the check') hints at a different behavior than the description's split operation, creating confusion rather than transparency.

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; every word earns its place. However, for a tool with four parameters and no annotations, this brevity borders on under-specification, so it does not quite reach a 5.

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?

With no annotations and no output schema, the description must carry the full invocation context. It explains only the hostname-splitting operation, leaves url/json/zone unintegrated, and says nothing about return format. An agent cannot confidently determine how to invoke the tool with the described purpose and the given schema.

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 description adds no parameter-level meaning beyond the schema: it only indirectly maps to the host parameter and never explains how url, json, or zone participate in the described hostname-splitting task. It does not add value, but it also does not misinform by itself.

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') and explicitly carves out a non-goal ('without WHOIS or ownership data'), which distinguishes it from enrichment tools. However, the tool's schema includes url, json, and zone parameters that do not obviously relate to hostname splitting, so the description alone leaves some ambiguity about the tool's true scope.

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 phrase 'without WHOIS or ownership data' provides an implicit when-to-use signal: choose this when you only need label splitting and not ownership enrichment. It does not name alternative tools or give explicit exclusions, and it gives no guidance on when to use the url, json, or zone parameters, so usage direction remains mostly implied.

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