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

Annotations already cover readOnly/idempotent/openWorld safety, so the description instead adds output shape ('each explained') and, more valuably, interpretive behavior: p=none legitimately passes Google/Yahoo requirements and quarantine is the stricter next step. This steers how the agent reports results, well beyond what the annotations declare.

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?

Front-loaded with the action and returned fields, then two tight advisory sentences. The policy interpretation sentences earn their place because they prevent a common wrong conclusion, though the second half is more advisory than definitional.

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?

No output schema exists, and the description compensates by describing what is returned and that tags are explained. For a single-parameter, read-only lookup this is nearly complete; only cross-tool routing 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?

Schema description coverage is 100% and the single 'domain' parameter is documented with an example in the schema, so the schema carries the load. The description adds no additional parameter detail; 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+resource: 'Look up and parse a domain's DMARC record', with the returned fields (policy, subdomain policy, percentage, alignment, reporting tags) enumerated. It is implicitly distinguishable from analyze_dmarc_report (which analyzes reports) and check_spf/check_dkim, though no sibling is named explicitly.

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 context is implied by 'look up and parse a domain's DMARC record' and reinforced by interpretation guidance for p=none vs p=quarantine. However, it never states when to prefer this over check_email_authentication, check_bulk_sender_requirements, or analyze_dmarc_report, so the agent must infer routing.

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