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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description still adds value by disclosing that this performs external DNS lookups and, more importantly, that the output includes remediation guidance ('explains what to fix'), which is behavior the annotations do not convey.

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 with zero filler; the core action is front-loaded and the second sentence supplies the motivating context and read-only guarantee.

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?

For a single-parameter read-only tool with no output schema, the description covers what it inspects, why it matters, and that it returns fix recommendations. It stops short of describing the report structure or any rate/scope limits, but nothing essential to invoking it correctly 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?

Only one parameter and schema coverage is 100%, with the schema already documenting it as 'Domain or email address, e.g. mon-entreprise.fr'. The description adds no further parameter detail, which is acceptable at this coverage level (baseline 3).

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 (checks) and the exact resource (SPF, DKIM and DMARC DNS records of an email domain), plus the goal (avoid spam placement). No sibling tool overlaps with DNS/email-authentication diagnosis, so an agent can select it unambiguously.

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 framing 'so that emails do not land in spam (Gmail and Yahoo sender requirements)', which tells the agent the diagnostic context. However, there is no explicit when-to-use statement, no prerequisites, and no comparison to alternatives.

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