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

Annotations only declare readOnlyHint and openWorldHint, so the description carries real weight here and does disclose important behavior: resolution happens via DNS-over-HTTPS, NXDOMAIN is reported, DNSSEC is validated, and a per-call price of $0.003 USDC on Base via x402 applies. That payment requirement is critical operational context absent from annotations. It stops short of rate limits or failure-mode details, so not a 5.

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?

Content is front-loaded: record types and TTLs first, derived hints next, transport and pricing last. Every clause conveys something actionable and there is no filler. It is dense but readable, with only the enumerated record list bordering on overlong.

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 must describe return values itself, and it does: records with TTLs, NXDOMAIN status, DNSSEC results, plus parsed SPF, CAA issuers and TXT verification-token services. Combined with the payment disclosure, an agent has everything needed to decide to call it and interpret the result.

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 100% and both parameters are documented inline, so the baseline of 3 applies. The description adds modest value by framing 'types' as a way to request only selected record types and by describing what the default set yields, but it omits SOA from the listed set even though the schema allows it, which slightly muddies rather than enriches parameter meaning.

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 opens with a specific verb+resource ('DNS lookup in one call') and enumerates exactly what is returned (A, AAAA, CNAME, MX, TXT, NS, CAA with TTLs, NXDOMAIN, DNSSEC). This clearly separates it from siblings like domain_whois, domain_email_check, and ens_resolve, which cover registration data, mail deliverability, and name resolution respectively.

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?

Usage is only implied: it is obvious you reach for this when you need raw DNS records, and the 'just the types you ask for' phrasing hints at narrowing scope. However, it never says when NOT to use it or names a sibling alternative (e.g. domain_whois for registrant data or domain_email_check for deliverability), leaving the agent to infer routing from sibling names alone.

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