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

Annotations already cover read-only, idempotent, non-destructive and open-world traits, so the description's job is to add more. It does so meaningfully by disclosing a real limitation: no SMTP connections are opened and catch-all domains therefore return valid, which is a false-positive warning an agent could not get from structured fields. It stops short of disclosing bulk-size limits or credit consumption.

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 sentences, nothing wasted; the check list comes first and the important caveat about SMTP and catch-all domains is placed immediately after it.

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?

With no output schema, the description could go further in indicating what a result looks like per address (verdict categories, reason codes) and any list-size limits. What it does cover — the verification signals and the catch-all caveat — is sufficient for an agent to call it 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?

There is a single parameter with 100% schema description coverage, so the schema already documents it; the baseline of 3 applies. The description adds a little context about what is done to those addresses but no format or batching constraints for the array.

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 (check) and resource (email addresses) and enumerates the exact checks performed: syntax, MX, disposable providers, role prefixes. This makes it distinguishable from lookup_mx or check_deliverability, though no sibling is named explicitly.

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?

Usage is implied rather than stated — an agent can infer this is the list-cleaning tool, but there is no explicit when-to-use, no when-not, and no pointer to alternatives such as plan_verification_waterfall or check_deliverability for cases needing SMTP-level validation.

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