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

Annotations already establish readOnly, idempotent and openWorld, so the safety profile is covered. The description adds real behavioral context beyond that: it discloses how DKIM is discovered (probing ~29 common selectors) and the concrete limitation that custom selectors are missed, which directly sets expectations about result completeness.

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 tight sentences, no filler. The mechanism and scope come first and the coverage limitation is appended concisely where it is most 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?

An output schema exists, so return-value detail is unnecessary here. The description covers what is fetched, how DKIM is discovered, and where results are incomplete, which is sufficient for correct invocation; only an explicit tie-breaker against dns_records is missing.

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 0% and the single 'domain' parameter carries no format detail in the schema. The description references 'a domain' but adds no syntax, apex/subdomain convention, or example, so it only partially compensates for the coverage gap on an otherwise self-evident parameter.

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?

Names a specific domain resource (SPF, DMARC, DKIM email authentication records) and the probing mechanism, so the agent knows exactly what is retrieved. The only gap is that it never explicitly contrasts with the sibling dns_records, which plausibly also surfaces TXT-based records, leaving the boundary to inference.

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 resource (auditing a domain's email authentication posture), but there is no explicit when-to-use guidance or named alternative such as dns_records. The 'custom selectors may not be found' line is a coverage caveat, not routing guidance, so it does not lift this above implied usage.

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