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

With no annotations, the description carries the full behavioral burden. It does disclose what is returned (registration/created date, age, registrar) and the payment model (trial calls per signed wallet), which is useful. It omits error/behavior details such as what happens for unregistered domains, RDAP lookup failures, or whether the wallet signature is required per call.

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?

Compact and front-loaded: the purpose and return payload come first, followed by the pricing note. The emoji and trial-call clause add minor noise but the whole thing is still one tight, scannable sentence.

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 no-annotation, no-output-schema tool with 0% parameter coverage, the description does compensate somewhat by enumerating return fields. But the unexplained dual string parameters and the absence of any failure/threshold context leave an agent with open questions before calling.

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 0% and there are two string parameters ('input' and 'domain') with no descriptions. The description implies a domain is supplied but never clarifies the relationship between the redundant 'input' and 'domain' parameters or their expected format (bare domain, URL, subdomain). This ambiguity is a real gap the description fails to close.

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?

States a specific verb and resource ('Fetches RDAP registration data for a domain') plus the concrete return fields (created date, age in years, registrar), which helps separate it from siblings like x402-domain-expiry or x402-registrar-lookup. It does not, however, explicitly distinguish itself from near-scope siblings such as x402-domain-intel or x402-domain-report, so it stops short of a 5.

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?

There is no when-to-use guidance and no mention of alternatives, despite a crowded domain-intelligence sibling set (domain-audit, domain-intel, domain-report, whois). The only contextual note is a pricing/quota line ('5 free trial calls per signed wallet'), which is not usage guidance.

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