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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safe read-only nature is known. The description adds value by detailing what the validation covers (syntax, MX, disposable, role-account), which is not in the annotations. 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 two sentences: the first defines purpose and scope, the second provides usage context. Every sentence is informative with no filler words or repetition.

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 simplicity (one param), the schema covers the parameter, annotations cover safety, and the description explains validation logic. The only missing piece is the return format (e.g., boolean vs. structured result), but that is a minor gap given the tool's nature. Overall, it is sufficiently complete for an agent to invoke 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?

The schema has 100% coverage for the single parameter 'email' with description 'Email address to validate'. The tool description does not add any extra parameter-specific meaning beyond the schema, so the 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 verb 'Validate' and the resource 'email address', and enumerates specific checks (syntax, MX records, disposable-domain, role-account detection). This makes it distinct from sibling tools like check_dmarc or verify_domain, which focus on different aspects.

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?

It provides clear scenarios: 'before sending' and 'Use this to protect sender reputation on imported lists.' It does not explicitly mention when not to use or alternatives, but the context is clear enough for an agent to decide. The usage guidance is practical and specific.

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