SPF, DKIM & DMARC Checker: Bulk Email Domain Security Audit

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

Annotations only declare read-only/open-world, but the description adds pricing ($0.002 per domain), the spending cap, timeout behavior and remediation advice (raise run_timeout_secs to 300, or shrink input). It also discloses the non-obvious billing quirk that run_max_items fills maxDomains and therefore limits what is charged, and warns that a missing DKIM result may be a false negative.

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 purpose and differentiation before the mechanics, and the return-field list is a compact enumeration rather than prose. It is dense — the behavior paragraph packs pricing, billing interaction, timeouts and output shape into one block — but nearly every sentence carries information an agent needs to call it correctly.

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 compensates by listing the per-item return fields (grade, score, spoofable, spfRecord, dmarcPolicy, fixes, status) and the response envelope {actor, count, items}. Cost, timeout, failure handling for unresolvable domains and the no-charge-for-empty-runs rule are all covered, leaving nothing material an agent would need to guess.

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 already 100%, so most parameter meaning is supplied structurally, but the description still adds value: it ties dkimSelectors to the false-negative risk, explains that domains are normalized and de-duplicated across bare domains/emails/URLs, and spells out the cross-parameter interaction between maxDomains and run_max_items that the schema alone does not convey. The remaining parameters are restated rather than deepened.

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 (audit email authentication for a list of domains) and enumerates exactly what is checked: SPF, DKIM, DMARC, MX provider, MTA-STS, TLS-RPT and BIMI, graded A-F. It then explicitly separates itself from company_website_enricher, ai_search_seo_audit and hidden_ai_instructions_scanner, so an agent can pick it out of the sibling set without opening a schema.

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?

Gives concrete triggers (deliverability or spoofing checks, a security prospect list, a vendor review) and explicit exclusions that route to named alternatives: SEO/AI-readiness goes to ai_search_seo_audit, page-level prompt injection goes to hidden_ai_instructions_scanner. Both when-to-use and when-not-to-use are covered.

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