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

No annotations are provided, so the description carries the full burden. It does disclose a non-annotated behavioral trait that matters: cost of 0.002 USDC per call via x402, plus the fact that it reads (not mutates) and returns flagged weaknesses. It stops short of describing the payment/auth handshake mechanics, error behavior, or limits, though the payment flow is partly covered by the schema field description.

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?

Two sentences, no filler: the capability and concrete checks come first, cost last. Every clause earns its place and the reader gets the essential picture immediately.

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?

With no output schema and no annotations, the description should explain the return shape; it does so at a high level (records, parsed policies, weakness flags) and adds pricing. Missing only finer detail on result structure and failure modes, which is minor for a single-domain read tool.

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 100%, so both parameters (domain, paymentProof) are already documented, including the 402 retry flow. The description adds no meaning beyond the schema, so baseline 3 applies.

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?

Specific verb and resource: reads SPF, DMARC and MX records for a domain, then parses policies and flags weaknesses. Clear about what comes back (records + policy assessment), which distinguishes it from a raw lookup. It never names the nearby siblings (dns_lookup, email_validate, whois), so the differentiation is inferable rather than explicit.

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 implied by the mention of auditing for missing DMARC, p=none, or SPF +all weaknesses, which tells an agent this is an email-auth security check. But there is no explicit statement of when to prefer this over dns_lookup, email_validate, or whois, and no prerequisites or exclusions.

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