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

With no annotations, the description carries the full burden. It does disclose useful behavioral traits beyond the schema – the result is a sorted nameserver list and calls are gated by a signed wallet with a 5-call free trial. It omits error behavior for invalid/nonexistent domains, rate limits, and whether the sort is deterministic.

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?

A single front-loaded sentence delivers the core purpose, with the trailing free-trial note kept brief. The emoji adds noise but the payload is tight and not bloated.

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 simple read-only lookup with no output schema, the description does state what is returned (a sorted nameserver list), covering the return-value burden. The unresolved 'input' vs 'domain' ambiguity and absent error/prerequisite context leave it only minimally complete.

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 0% for two parameters, and the presence of both 'input' and 'domain' is unexplained. The description implies a domain is required but does not clarify what 'input' is for or how the two fields relate, so it fails to compensate for the documentation 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 and resource: 'Resolves a domain's NS records and returns the nameserver list sorted.' This distinguishes it from DNS siblings like x402-mx-lookup or x402-txt-lookup by record type. However, it never explicitly names an alternative, so the differentiation is inferred rather than stated.

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?

There is no when-to-use guidance, no prerequisites, and no mention of when a sibling such as x402-dns-lookup or x402-dns-all would be preferable. The only additional context is promotional ('5 free trial calls per signed wallet'), which is pricing, not usage direction.

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