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

Annotations already establish the safe-read profile (readOnlyHint, idempotentHint, destructiveHint=false), so the bar is lower. The description still adds genuine behavior beyond them: it returns an explanation, not just a record, and actively flags weaknesses like p=none or missing external report authorization. It does not say what happens when no DMARC record exists or how DNS failures are surfaced.

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?

One sentence, front-loaded with what is retrieved and followed by the analysis performed; the parenthetical field list is dense but each item earns its place. No filler or restating of the title.

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 responsibly names the returned components (policy, pct, rua/ruf, alignment) and the weakness annotations, which is most of what a caller needs. The remaining gap is edge-case behavior on missing or malformed records, minor for a single-parameter read tool.

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 with 100% schema description coverage ('Domain (example.com)'), so the schema carries the semantics. The description adds nothing about the domain parameter (e.g., whether a subdomain or full URL is accepted), which is the expected baseline-3 outcome.

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?

Uses a specific verb pair ('find and explain') on a specific resource ('the DMARC record of a domain') and enumerates the fields analyzed (policy, pct, rua/ruf, alignment). An agent can readily distinguish this from sibling checks like spf_lookup or dkim_check by the record type, though the description never explicitly contrasts itself with 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?

Usage is only implied: the tool is for inspecting DMARC posture on a domain, and the weakness-flagging clause hints at audit use. There is no explicit when-to-use vs. when-not guidance and no pointer to sibling tools such as spf_lookup or domain_health_report that might cover adjacent needs.

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