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

Annotations already declare read-only, open-world, non-idempotent, and non-destructive behavior. The description adds useful context beyond annotations: payment and auth via x402 USDC or a card key, per-call cost, the first 25 free, failed calls free, and that repeats are charged. It still does not describe data freshness or failure modes in detail, but it meaningfully covers cost and access behavior.

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 front-loaded and organized around outputs, use cases, the alternative tool, and cost. It is somewhat dense and repeats the read-only safety point already covered by annotations, but the extra payment and free-tier details are relevant for a paid tool.

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 complex multi-source domain lookup with no output schema, the description enumerates the returned intelligence and covers usage, the key alternative, pricing, auth, and safety. It is complete enough to select and invoke, though it does not specify response shape or edge-case behavior.

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 single required parameter is fully documented in the schema with an example, and the description repeats the same example without adding format constraints such as IDN support, subdomain handling, or URL rejection. With 100% schema coverage, the baseline of 3 is appropriate.

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 names a specific resource and enumerates the exact data it aggregates: DNS record types, DNSSEC status, registrar and registration dates with domain age, and SPF/DMARC email authentication. It also explicitly distinguishes itself from domain_report for a flagged trust verdict, so an agent can tell what this tool is and is not.

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?

It provides concrete use cases such as lead qualification, phishing and trust checks, and deliverability audits, and it names domain_report as the alternative when a trust verdict with named flags is needed. It does not explicitly address other relevant siblings like dns_lookup or state when not to use this broader paid lookup, so the guidance is clear but not exhaustive.

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