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

Annotations already declare readOnlyHint=true, idempotentHint=true and non-destructive, and the description adds real context beyond them: the 10-lookup limit estimate for SPF, that output is host/type/value pairs to publish, and that it generates rather than publishes. The phrase 'It writes records' is slightly loose against readOnlyHint, but the surrounding 'Returns host, type and value to publish' makes clear it produces text and does not mutate DNS, so it is not a true contradiction.

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?

Three tight sentences with zero filler, front-loaded with the primary generator action and closing with the routing rule. Every clause carries information.

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 nine optional parameters and no output schema, the description usefully discloses the return shape (host, type, value) and the lookup-estimate feature. It could say a bit more about how partial inputs are handled (e.g., calling with only dmarcPolicy), but nothing essential is missing for correct invocation.

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% with enums and defaults documented, so the schema carries parameter meaning. The description adds only the lookup-limit framing around spfProviders; it does not explain the interplay of dmarcPolicy, dmarcPct, or subdomain policy beyond what the schema already says. Baseline 3 is appropriate.

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 specific verbs and resources: writing an SPF record from sender providers, a DMARC record from a policy, and DKIM publication location. Explicitly contrasts itself with the check_spf/check_dmarc/check_dkim siblings, so an agent can distinguish generator from checker without opening schemas.

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 an explicit when-not rule: 'to check what is published, use check_spf, check_dmarc and check_dkim,' naming the alternatives directly. This is the key routing decision for this tool and it is spelled out, not implied.

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