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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is clear. The description adds valuable behavioral context: it does not perform DNS lookup, it returns parsed tags and level'd findings, and it instructs to present any returned record verbatim. It also explains a policy nuance about p=reject being unlocked only by aggregate-report evidence, which is useful for setting expectations. Minor gap: it doesn't explicitly state whether the tool can return errors for malformed input, but the schema and output schema likely cover that.

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 concise and front-loaded with the primary use case. It packs a lot of useful information into a few sentences. The only slight inefficiency is the detailed policy explanation about p=reject and aggregate-report evidence, which is relevant but could be seen as slightly verbose for a tool description. Overall, every sentence earns its place.

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 has a single parameter, a rich output schema, and clear annotations, the description is complete. It covers what the tool does, how to invoke it, what it does not do, and how to handle the returned record. An agent has everything needed to select and call this tool correctly.

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%, so the schema already documents the `record` parameter well. The description adds extra meaning by clarifying that the record value only should be passed, not the _dmarc hostname, and by giving an example. This goes beyond the schema's description and helps prevent a common mistake.

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 clearly states the tool's purpose: validate a pasted DMARC record and report parsed tags, level'd findings, and validity. It explicitly distinguishes itself from related tools like `upgrade_record` and `scan_domain` by noting it does not perform DNS lookup and takes the record string itself.

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 explicit when-to-use guidance: 'Use this when the user pastes a DMARC record and asks whether it is valid, correct or safe.' It also gives exclusions: 'No DNS lookup — pass the record string itself.' It names an alternative (`upgrade_record`) and explains when that tool is appropriate, which helps an agent choose correctly.

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