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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is covered. The description adds a real behavioral fact beyond them: it 'triggers a fresh DNS lookup', telling the agent results reflect live state rather than cache and that the call touches external DNS. Auth, rate-limit, and latency characteristics remain unstated.

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 the scope (which record types) front-loaded and the fresh-lookup caveat second. No filler and nothing that repeats the schema or annotations.

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 read-only, fully annotated, two-parameter check tool with no output schema, the description covers what is inspected and that results are live. It would be stronger if it sketched the return shape (per-record status) or pointed to the sibling that reports account-level deliverability.

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% with 2 parameters, both documented (domainId, apiKey override). The description adds no syntax, format, or sourcing detail about domainId or the API key, so the baseline 3 applies.

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?

Specific verb (check) plus resource (DNS health of a domain) and it enumerates exactly what is verified: DKIM, SPF, DMARC, MX. An agent knows precisely what this returns, though it does not name a sibling (e.g., get_deliverability_status) to differentiate from.

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?

No when-to-use guidance, no prerequisites, and no alternative named despite close siblings like get_deliverability_status and list_domains. The closest thing to guidance is the implied obviousness of a health check, which is not explicit routing advice.

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