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

Adds substantial behavior beyond the annotations: per-call price ($0.005 USDC on Solana), the x402 payment challenge/retry protocol, and an HTTP fallback URL. This also explains why readOnlyHint=false is plausible despite the word "lookup" — the call spends funds. Missing only rate limits or response-shape details.

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-loads the purpose in the first clause, then the cost and payment mechanics, then the HTTP equivalent. Dense but every sentence carries operational weight; no filler.

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 two-parameter lookup with no output schema, the description covers purpose, cost, and the exactly-once payment flow an agent must follow. The one gap is not describing the response payload (record data/TTL), which matters slightly more given there is no output schema.

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%, so both parameters (domain, type with default A) are already documented in the schema. The description mentions no parameters directly; the {domain} in the HTTP equivalent only echoes the schema. Baseline 3 applies since the schema does the work.

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?

Names a concrete verb and resource ("DNS lookup") plus the transport mechanism (DNS-over-HTTPS), which is more specific than the bare name. It does not explicitly distinguish itself from nearby devutils siblings such as devutils_rdap or devutils_ip, but the operation is unambiguous on its own.

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 strong procedural guidance for the payment handshake (call unpaid, read the PaymentRequired challenge, retry with _meta["x402/payment"]), but nothing about when to prefer this tool over devutils_rdap or devutils_ip, or when DNS resolution is the right call. Usage is implied by the tool's purpose rather than stated.

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