Validate email addresses

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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint false, so the safety profile is covered. The description adds meaningful behavioral context: it performs multiple checks, returns a reason when invalid, and is limited to 100 addresses. It does not contradict the annotations and provides value beyond them.

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 a single, well-structured sentence that front-loads the core action and scope ('Checks up to 100 email addresses without sending mail') before enumerating specific checks. Every word adds value, and there is no redundancy or padding.

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 an output schema (which handles return values) and only one parameter with clear semantics, the description covers all necessary context for an agent to decide when to use it and what to expect. It mentions the validation types and the reason-on-invalid behavior, making it complete for this simple tool.

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 no description for the single 'emails' parameter (0% coverage), so the description carries the burden. It explains that the tool checks up to 100 addresses and what those checks are, which clarifies the expected input format (array of email strings) and behavior. This compensates well for the missing schema description.

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 uses a specific verb ('Checks') and resource ('email addresses'), and enumerates the exact validation dimensions: syntax, MX, disposable providers, role accounts, and typos. This clearly distinguishes it from sibling tools check_addresses and check_phones, making its 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 explicitly states it checks without sending mail, which signals it is a validation-only tool and not for deliverability testing. It doesn't name alternatives or exclusion criteria, but the sibling names make it clear when to use this over check_addresses/check_phones, so the context is adequate.

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