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

Adds substantial context beyond the annotations (readOnly/openWorld/idempotent/non-destructive): the exact data sources (IANA RDAP bootstrap, TLD registry RDAP, own resolver, no third-party DoH relay), a 30-minute cache, that raw is honestly null, and the full payment model where the calling wallet pays and the server never holds a wallet. These are non-obvious traits an agent needs to call it correctly.

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?

Dense but well front-loaded: the paid marker and one-call value proposition come first, followed by data sources and payment mechanics. Some redundancy — the $0.012 USDC / x402 payment terms appear both at the start and the end — but nearly every sentence carries real information.

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?

Despite there being no output schema, the description explains return contents (RDAP fields, email-auth records, posture summary, additive aliases, null raw), sources, caching, and the payment precondition. Nothing an agent needs to invoke it correctly is missing.

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 100%, so both parameters (domain and the nested payment_header) are already fully documented in the schema, including the two-step payment handshake. The description's parameter-relevant content merely restates the payment flow, so the baseline 3 is appropriate when the schema does the heavy lifting.

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 ('Domain identity & trust posture in one call') and enumerates exactly what is returned: RDAP registration data, live DNS email-auth (MX/SPF/DMARC/NS), and a heuristic posture summary. An agent can clearly separate this from siblings like domain_intel_preview or email_validate 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 description gives a concrete paid-workflow instruction ('Call with no payment_header first to receive the payment requirements... call this same tool again with the SAME business arguments'), which is useful usage guidance. However, it never says when to prefer this over the sibling preview tool or email_validate, so alternative-selection guidance is absent.

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