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

Annotations already declare readOnly, openWorld and non-destructive, but the description adds genuinely new behavioral context: the fixed USD 0.002 per-call cost, the x402/USDC-on-Base payment path, and that failed calls are not charged. That pricing and billing detail is exactly what structured fields do not convey.

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?

Two tight sentences: the payload comes first, the cost model second, with no filler. Sizing is appropriate for a single-parameter lookup.

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 one-parameter read tool, annotations cover safety and the description covers output fields and billing. The missing piece is the domain parameter's expected format and any sibling routing, which leaves a real gap despite the otherwise solid coverage.

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 0% and there is one required parameter (domain) that the description never characterizes. It does not say whether the value should be a bare domain, a subdomain, or include a scheme, so the description fails to compensate for the empty schema.

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+resource (retrieve domain registration data via RDAP) and enumerates the returned fields (registrar, dates, status codes, nameservers, DNSSEC). It is clear what the tool does, but it never differentiates itself from the sibling dns_lookup, so an agent must infer the boundary itself.

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 explicit when-to-use or when-not-to-use guidance, and the most relevant alternative, dns_lookup, is never mentioned. Usage is only implied by the RDAP content listed, leaving the agent to guess whether registration data vs DNS resolution is the right call.

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