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 value by detailing the specific DMARC fields returned (enforcement, alignment, reporting) and notes it is 'part of the scan_domain audit,' which gives context about its role. No contradictions 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 three sentences with no wasted words. The first sentence states the core action and resource, the second elaborates on returned fields, and the third provides usage guidance and sibling differentiation. Information is front-loaded and 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 3 parameters (all documented in schema), an output schema, and clear annotations, the description covers what is needed: purpose, output specifics, usage context, and distinguishing from related tools. The agent can confidently invoke this tool without additional clarification.

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 baseline is 3. The description does not add extra meaning for the parameters (domain, format, force_refresh) beyond what the schema already provides. It mentions 'domain' implicitly in the first sentence but offers no additional details on formatting or caching behavior. The schema itself is sufficient, so 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 action ('Look up and validate the DMARC record for a domain') and lists specific outputs (enforcement level, alignment mode, reporting destinations). It explicitly distinguishes from two sibling tools (check_shadow_domains and assess_spoofability), making the tool's purpose unambiguous.

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 use cases: 'determine a domain's DMARC enforcement level, whether it sends aggregate reports, or if it is protected against email impersonation.' It also names two distinct alternatives and explains what they check. While it does not state when NOT to use this tool, the positive guidance is strong enough for an agent to select appropriately.

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