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

Annotations already cover the read-only, idempotent, non-destructive profile, and the description adds genuinely new context: it is privacy-safe and costs $0.001 native USDC on Base, which tells an agent a payment step is involved. It stops short of describing payment failure handling or rate limits, so it falls one notch below the top.

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 sentences, zero filler, with the capability statement front-loaded and the cost constraint second. 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 one-parameter lookup with no output schema and solid annotation coverage, the description covers what is returned and the payment requirement. Minor gaps remain around input format expectations and error/refund behavior on a paid call.

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?

With a single required 'domain' parameter at 0% schema description coverage, the description must carry semantics, and it only implicitly identifies the input as a domain. It never clarifies accepted format (registrable domain vs subdomain vs IDN) despite the schema imposing min/max length bounds.

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 ('lookup') and resource ('RDAP/WHOIS-successor') and enumerates the exact payload (age, expiry, registrar, statuses, nameservers, DNSSEC) so an agent can distinguish it from domain_email_security and the *_preflight siblings without opening a schema.

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 enumerated return fields imply the use case (registration/DNS delegation data, not email-auth checks), but there is no explicit when-to-use or when-not-to-use guidance and no sibling named as an alternative. Usage is left to inference.

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