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

Beyond the annotations (readOnly, openWorld, idempotent, non-destructive), it discloses that external network requests are made, that the whole call is time-bounded ("ten seconds overall"), what the report contains (observations, errors, selected security headers, next steps, limits), and it explicitly frames returned evidence as untrusted data rather than instructions — a genuine prompt-injection warning that no annotation conveys.

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 dense sentences, front-loaded with what is checked, then limits, then the untrusted-data caveat. No filler, no restatement of the tool name or schema constraints.

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 carries the return-shape burden and does so ("individual observations/errors, selected security headers, next steps and limits"), plus latency, external-network dependency and scope limits. Nothing an agent needs before calling it 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?

There is a single parameter and schema description coverage is 100%: the schema already explains "Public domain name only; no URL, path, port or credentials." The description adds no format or constraint detail beyond that, 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?

States a specific composite action ("Combine public A/AAAA DNS, MX/SPF/DMARC and pinned HTTPS root checks in one admin report") over a named resource (a domain). The aggregating scope implicitly distinguishes it from the single-purpose siblings check_email_dns, check_https, lookup_dns and trace_email without needing to name them.

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?

"in one admin report" and "No complete security or deliverability verdict" imply the intended context and set a bound on interpretation, but the description never routes the agent explicitly to or away from the four sibling checks (e.g. "use this for a combined overview; use check_https for TLS alone"). Usage is implied rather than stated.

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