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

Annotations only say readOnly=true and openWorld=true; the description adds the material behavior the annotations cannot convey: a 0.005 USDC x402 charge on Base, a required two-call payment handshake, and a real limitation that DKIM is only probed at 10 common selectors so custom selectors may be missed. It also discloses output shape (score, issues, next record) and that sp/ruf/fo are preserved in the suggested record.

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 vendor, price, and the core capability, then input, then transport, then payment flow. Dense but nearly every clause carries load; the bracketed pricing prefix and raw endpoint URL add some clutter at the front, though both are operationally relevant.

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, and the description compensates by naming what comes back (0-100 score, issues, exact next DMARC record). Combined with the payment protocol and the known DKIM limitation, an agent has everything needed to invoke it correctly 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%, so the baseline is 3; the description goes further by showing the literal q payload shape ({"domain":"example.com"}) and by explaining the ordering semantics of x_payment, which the schema alone does not (it only says it is 'the terms returned on the first call'). The HTTP GET URL with the q parameter reinforces how q is passed.

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 chain: a live DNS check covering DMARC policy, SPF recursion depth, DKIM selector probing, and MX, returning a 0-100 score plus a suggested next record. The scope (audit + remediation record generation) is unambiguous and cannot be confused with any sibling tool in the list.

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?

Explicitly names the target caller ('For agents that send mail as a domain') and outlines the two-step payment protocol: call once without x_payment for terms, call again with x_payment for the result. No competing DMARC/SPF sibling exists to route against, and no explicit when-not-to-use case is given, which keeps it just below a 5.

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