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

With no annotations, the description carries the full disclosure burden. It does add real behavioral context the schema cannot: the cost model ('x402 price $0.02/call (USDC, eip155:8453)') and the authoritative-registry provenance. However, it omits error/failure behavior (e.g., unregistered domains), rate limits, and any explicit statement that the lookup is read-only and payment-gated before the call succeeds.

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?

It is front-loaded with the returned fields, then the use case, then pricing — a sensible order with little waste. It loses a point for the garbled 'Use this when an agent needs to registrar, dates, nameservers' clause, which reads as a truncated sentence and slightly muddies the middle.

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?

With no output schema, the description takes on the job of describing return values, and it does so thoroughly by listing every field the record contains. Combined with the provenance and pricing notes, an agent has enough to call it correctly; only error/payment-flow behavior is left uncovered.

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?

There is a single parameter ('domain') and schema description coverage is 100%, so the schema already documents it. The description adds nothing about expected input format (FQDN vs bare name, IDN, subdomains), so the baseline of 3 for a fully-covered schema is the correct ceiling here.

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 verb (lookup) and resource (domain registration record) and enumerates the exact fields returned: registrar, creation/expiration/last-updated dates, nameservers, EPP statuses, DNSSEC. It implicitly separates itself from DNS/MX/SSL siblings by framing the output as 'registry data' from the 'authoritative registry', but it never names a sibling tool, so the differentiation is inferential rather than explicit.

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 sentence 'Use this when an agent needs to registrar, dates, nameservers — registry data' gives a when-to-use trigger, but it is grammatically broken (missing the verb) and offers no when-not guidance or named alternatives such as live_dns_lookup or security_mx_lookup. Usage is implied rather than routed.

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