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

Annotations cover read-only and open-world, yet the description adds substantial behavioral context they don't: deterministic DNS-over-HTTPS, no AI, per-call pricing ($0.003 USDC via x402 on Base), and a free tier (first 5 calls/day/client). This pricing/rate-limit/payment detail is exactly the context an agent needs before invoking.

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 dense sentence, but it is front-loaded with the resource and each clause (check list, determinism claim, pricing) carries information. It is tightly packed rather than padded, though the enumeration-heavy style is borderline crowded.

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, the description carries the burden of conveying what comes back, and the enumerated check list plus the 'readiness verdict' gives a solid content overview. It stops short of describing the response format or structure, which is the one remaining gap for a report-style 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 coverage is 100% so the baseline is 3, and the description exceeds it by explaining the default-vs-custom selector behavior: DKIM keys are probed at 'common selectors or your own via selectors='. That default behavior is not evident from the schema alone, adding real 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?

States a specific verb+resource ('Full email-auth report for a domain') and enumerates exactly which checks it covers (SPF, DMARC, DKIM, MX, MTA-STS, TLS-RPT, BIMI, bulk-sender verdict). The 'full report' framing plus the enumerated scope implicitly distinguishes it from the narrower siblings dmarc_check and spf_lookup_count.

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?

The word 'Full' and the check list imply this is the comprehensive umbrella option versus the single-check siblings, and the bulk-sender verdict hints at its intended use case. However, it never explicitly says when to prefer this over dmarc_check or spf_lookup_count, nor names any exclusion, so routing is left to inference.

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