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

Annotations already declare readOnly/non-destructive/idempotent/closed-world, so the safety profile is covered. The description adds real behavioral value beyond that: this is pure string parsing with no DNS lookup, and its output must be presented verbatim. The p=quarantine/p=reject explanation clarifies the policy-upgrade boundary that motivates why a static pasted record can't unlock stricter policies.

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 usage trigger and output summary are front-loaded and efficient. The trailing discussion of `upgrade_record` and p=reject is longer than strictly needed for this tool, though it earns some place by explaining the 'safe' framing in the trigger.

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 annotations covering safety and an output schema covering return shape, the description only needs to supply the trigger, the no-DNS input constraint, and the verbatim-presentation obligation — all of which are present. Nothing an agent needs to invoke this correctly 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 coverage is 100% and the single `record` parameter is fully documented in the schema, including the 'value only, not the hostname' constraint. The description reinforces but does not extend that semantics ('pass the record string itself'), so baseline 3 is appropriate.

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 verb (validate) and resource (DMARC record), then immediately enumerates what it produces: parsed tags, leveled findings, and a validity verdict. It also names a sibling (`upgrade_record`) so the agent can tell the two apart without opening either schema.

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 opening sentence gives an explicit trigger — 'when the user pastes a DMARC record and asks whether it is valid, correct or safe' — and the 'No DNS lookup — pass the record string itself' line routes away from DNS-based siblings. It does not, however, distinguish this from other parsing siblings like parse_dmarc_report or check_record, so it falls short of full when-not coverage.

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