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

Since no annotations are provided, the description carries the full burden of disclosing behavior. It lists exactly what the tool returns (registered_at, expires_at, nameservers, email-forwarding status) and enumerates possible statuses ('active / pending verification / pending NS propagation / etc'), giving the agent a clear picture of the output. While it doesn't mention error handling or rate limits, the disclosure is detailed for a lookup tool.

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 concise and well-structured: it opens with the primary purpose, lists key return fields, and ends with a 'WHEN TO USE' section containing concrete examples. Every sentence carries informational value, and the 'WHEN TO USE' label improves scannability.

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 output schema, the description appropriately explains return values (registered_at, expires_at, nameservers, email-forwarding status). It also includes common user intents, covering likely use cases. It could mention behavior when the domain is not found or not owned, but for a single-parameter lookup tool, the description is largely complete.

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 provides a comprehensive description for the single parameter: 'A domain previously registered via register_new_domain.' With 100% schema coverage, the description adds no additional parameter semantics. Per the rubric, baseline is 3 when schema coverage is high, and no extra value is needed.

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 tool's function: 'Look up the registration status of a domain you previously registered through MCPDomain.' It specifies the exact resource (domains registered via MCPDomain) and the verb 'look up,' which distinguishes it from sibling tools like check_domain_availability (which checks availability before registration) and configure_domain_dns/email (which modify settings).

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 provides explicit usage scenarios under 'WHEN TO USE' with example user questions like 'is my domain ready?' and 'did email forwarding finish setting up?'. This gives clear context for when to invoke the tool. It does not explicitly name alternatives or state 'when not to use,' but the phrase 'previously registered' implies exclusions (e.g., not for availability checks), providing some differentiation.

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