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

Annotations already declare readOnlyHint and openWorldHint, yet the description adds two genuinely non-obvious traits: judgment is domain-list based and performs no mail server lookup (so an unlisted-but-dead mailbox still passes), and the call costs 20 points. That cost and the no-lookup limitation are exactly the kind of context annotations cannot carry.

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 content is compact and every element (scope, output fields, no-lookup caveat, price) earns its place. The full duplication in English and Korean doubles the length for the same information, and the pricing note is buried at the end rather than surfaced earlier.

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 correctly takes on the burden of describing return values (per-address flags plus a high/medium/low risk grade). Combined with a read-only annotation profile and a fully documented single parameter, the only real gap left is the exact partial-failure behavior for invalid entries in the batch.

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 coverage is 100% for the single 'emails' parameter, and the schema already documents the newline/comma delimiting and the 100-item cap. The description restates the cap but adds no parsing rules — e.g. what happens when more than 100 are supplied or how malformed entries are reported — so baseline 3 applies.

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 concrete verb and resource ('Check up to 100 emails at once') plus the exact output fields (syntax, disposable, free, role-account flags, risk level). The batch scope implicitly separates it from the single-address check_email_valid sibling, but it never names that sibling, so the differentiation is left for the agent to infer.

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 100-address cap and input format signal a batch use case, but there is no explicit 'use this instead of check_email_valid when…' statement and no when-not guidance. Usage is only implied by the scope wording.

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