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

Goes well beyond the annotations: it quantifies the cost (1 credit per email), warns of a possible saved-card charge, notes test_ keys spend nothing, states the batch cannot be cancelled here, and explains why the openWorld/non-idempotent call is never retried. These are the exact operational risks the destructiveHint and idempotentHint flags hint at but do not explain.

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 cost warning is front-loaded in caps and every subsequent sentence carries a distinct load: billing behavior, key type, cancellation/retry policy, return value and polling path, and compliance scope. No sentence is filler.

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?

For a non-idempotent, credit-spending, open-world mutation with no output schema, the description covers cost, failure recovery, return shape ('returns the batch id'), and the follow-up tool. Nothing an agent needs before invoking or after failing is missing.

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 emails, confirm, retries, and response_fields, including the 1-5000 bound and the const:true confirm requirement. The description's 'up to 5000 email addresses' restates the schema's maxItems and adds no syntax or default detail for retries or response_fields. 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 specific verb and resource ('starts a bulk verification of up to 5000 email addresses') and immediately marks it as credit-spending, which cleanly separates it from emailable_verify_email (single address) and emailable_get_batch (polling). The agent can route correctly without opening any schema.

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?

Explicitly names the alternatives and the conditions that select them: poll with emailable_get_batch, and if the call fails or times out check emailable_get_account before retrying. It also states when NOT to blindly retry, with the reason (double charge).

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