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

Beyond readOnlyHint=true and openWorldHint=true, it discloses operational behavior an agent could not infer: revoked keys and CNAME-delegated keys are reported, up to 8 common selectors are probed when no selector is supplied, and it makes no message-alignment judgment. It also states the commercial terms ($0.002 USDC per successful call via x402 across Base/Solana/Arc, failed calls not charged), which is important pre-invocation context for a paid endpoint.

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 front-loaded paragraph that opens with exactly what is fetched, then scope limits, then the sibling redirect, then pricing. Every sentence carries information; the pricing/chain enumeration is the only part that runs slightly long relative to the tool-selection task.

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 only two parameters, full schema coverage, an output schema, and readOnly/openWorld annotations, the description covers everything needed to decide and invoke: scope, exclusions, selector fallback, key states reported, cost, and one alternative. The only gap is that it does not say how results are structured when several record types or multiple selectors resolve, though the output schema plausibly carries that.

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 are already documented, making 3 the baseline. The description adds a little beyond the schema by quantifying the empty-selector fallback ('8 common selectors') and noting that revoked and CNAME-delegated keys surface in results, but it adds no naming convention or format guidance for the selector string itself.

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 names three specific artifacts: DMARC policy fields (p, sp, pct, rua), the SPF record and its all-mechanism, and DKIM keys for a given or common selector, against a specific resource (published DNS records for a domain). It also names one sibling it is not (security_dkim_key_checker). It does not differentiate from broader siblings like security_dns_records or security_bimi_record_audit, which also touch TXT/policy records, so the sibling separation is only partially done.

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?

It gives both a positive scope ('Reads the published DNS records only') and an explicit exclusion ('it does not check alignment against a real message'), plus redirects to security_dkim_key_checker for the single-key need. It stops short of stating when a DMARC/SPF/DKIM audit should be preferred over the generic DNS or BIMI audit siblings, so the routing guidance is clear but not exhaustive.

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