validate_emails

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

With no annotations, the description carries the full burden. It does disclose the actual operations (syntax, disposable/role detection, live DNS-over-HTTPS MX/A lookup) and that MX checking is optional and slower, which is useful. However, it says nothing about cost, rate limits, external network calls' failure modes, or permissions.

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?

Two tight sentences: the mechanics come first, the use case second, with no filler or redundancy.

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?

There is no output schema and no annotations, so the description should ideally characterize what a validation result looks like (per-address verdicts, reason codes, what happens to invalid entries). The operations are covered but the return contract is left entirely unspecified.

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 all three parameters including the 'overrides email when non-empty' rule and the checkMx default. The description only restates the MX lookup as optional, adding marginal meaning, so the 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+resource (validate e-mail addresses) and enumerates the three checks performed: syntax, disposable/role detection, and optional MX/A lookup. It does not explicitly differentiate itself from the sibling check_email_security, which is a plausible source of confusion.

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 phrase 'Good for cleaning a lead list before sending' implies a usage context, but there is no explicit when-to-use/when-not guidance and no mention of the neighboring check_email_security tool, which an agent might otherwise choose.

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