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

Annotations already cover readOnlyHint, idempotentHint, and destructiveHint, so the safety profile is known. The description adds valuable behavioral context: the meaning of 'unverified' and 'not_applicable' statuses, and the auth-gated pdfUrl requiring a bearer token. No contradiction with annotations.

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?

The description is a single dense paragraph with many details. Each clause adds operational value (e.g., explaining scoreSubtitle, status meanings, PDF auth), but the long run-on sentence structure makes it slightly harder to parse. Still, nothing feels wasted.

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?

Given the tool's complexity and the absence of an output schema, the description thoroughly enumerates all return fields (score, grade, scoreSubtitle, check statuses, top issues, blocklist count, DMARC policy, pdfUrl) and explains ambiguous statuses. It is complete enough for an agent to invoke and interpret results.

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 only one parameter ('domain') and the schema describes it completely with an example. The description does not add additional meaning beyond the schema, so the baseline of 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?

The description uses a specific verb ('Return') and identifies the resource ('structured deliverability report') with clear scope ('for a tracked domain'). It distinguishes itself from sibling tools like get_deliverability_score (score only) and get_dmarc_summary (DMARC-specific) by enumerating the full report contents.

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?

The description provides a clear use case: 'Use this to summarize a domain's posture or hand a client a report.' It does not explicitly mention when not to use it or name alternative tools, but the context is sufficiently clear for an AI agent to decide.

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