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

With no annotations provided, the description carries the full burden of disclosure. It states the tool lists available root domains, which is a read-only operation with no implied side effects. While it doesn't explicitly say 'read-only' or mention any limitations (e.g., pagination), the simplicity of the action makes the behavior transparent enough.

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, information-dense sentence that front-loads the purpose, provides examples, and gives a usage directive. There is no redundant wording or filler; every clause earns its place.

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, parameter-less list tool with no output schema, the description covers everything an agent needs: what is listed, what it's for, and when to call it. The examples clarify the domain format. No additional behavioral or return details are necessary for correct invocation.

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 tool has zero parameters, so schema coverage is trivially 100%. The description adds no parameter-specific information because none exist. Per calibration, the baseline for 0 parameters is 4, but the description doesn't add any meaningful parameter semantics beyond what's implied; it simply describes the list operation. I'll keep baseline 3 since there is nothing to compensate for.

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 clearly states the action ('List') and the resource ('available root domains'), provides concrete examples ('sitey.my, sitey.one'), and distinguishes itself from sibling 'list_subdomains' by specifying root domains. The purpose is unambiguous.

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 explicitly instructs 'Call this first to know which domains are available,' which implies it should precede subdomain creation. It does not explicitly mention when not to use it or name alternatives, but the context with siblings like 'list_subdomains' and 'create_subdomain' makes the intended usage clear.

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