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

Annotations already cover read-only, open-world, idempotent, and non-destructive behavior. The description adds valuable context about the DKIM lookup being 'best-effort' and the caveat that a missing DKIM match does not prove absence, which is important for interpreting results. This goes beyond the 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 two sentences, with the core action and scope front-loaded, followed by an important caveat and a clarifying note. No wasted words; every sentence adds value.

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?

For a single-parameter tool with full schema coverage and no output schema, the description provides a clear picture of what the tool does, its limitations, and its scope. It could potentially mention the output format or expected return values, but given the simplicity and annotations covering safety, it is nearly complete.

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 parameter 'domain' is already well-documented. The description reinforces that it's a domain (not an address) and gives an example, but doesn't add significant new semantic meaning beyond the schema. Baseline of 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?

The description clearly states the tool's purpose: auditing a domain's email anti-spoofing setup, explicitly listing SPF, DMARC, and DKIM. It differentiates itself from sibling tools like email_validate or email_verify by emphasizing it checks a domain, not a single address, and focuses on anti-spoofing rather than address deliverability.

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?

While it doesn't name specific sibling tools, it provides clear context on when to use it (domain-level anti-spoofing audit) and implicitly excludes single-address checks. The clarification 'Checks a domain, not a single address' effectively guides agents away from using it for individual email validation, though it could be more explicit about alternatives.

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