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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds genuinely new behavioral context: a per-call cost of $0.002 USDC via x402 and the fact that three independent resolvers are consulted and compared. It does not mention rate limits or response shape, but the payment disclosure is the important non-obvious trait here.

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?

Front-loaded with the core capability, followed by the reverse-DNS hint and cost. Dense but nearly every clause carries information; the record-type enumeration is slightly long but defensible as it defines scope.

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?

There is no output schema, so the description carries the return-value burden, and it does so reasonably by naming propagation agreement, DNSSEC status, SPF and mail provider. Payment and reverse-DNS behavior are covered; only output structure and error behavior are unstated.

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 coverage is 67%: type and compare are documented in the schema, but the required `name` parameter has no description. The description partially compensates by implying `name` accepts a hostname or an IPv4 for reverse lookups, and it lists valid record types that overlap the `type` default. Baseline 3 is appropriate given the partial gap.

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 (DNS records) with explicit scope: three named resolvers queried at once. It enumerates the record types and the extra analyses (propagation agreement, DNSSEC, SPF, mail provider), which clearly separates it from siblings like domain, domain_audit, ip, or report_domain.

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?

"Give an IPv4 for reverse DNS" is a concrete usage instruction for one mode, but there is no when-to-use/when-not guidance and no routing to or from siblings such as domain or domain_audit. Usage is implied rather than stated.

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