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

Annotations only declare readOnlyHint=false and openWorldHint=true; the description goes well beyond by disclosing asynchronous execution, credit reservation with later settlement, the API-key auth requirement, and the returned payload keys. The one gap is that 'up to N credits' never ties N to the email count.

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?

Five short sentences, each adding a distinct fact: purpose, cost behavior, polling path, callback option, auth, and return shape. No filler and the core action is front-loaded.

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 usefully enumerates the return fields, and it covers the async lifecycle, credit model, auth, and follow-up tool needed to complete the workflow. Nothing essential for correct invocation 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 0%, so the description must carry the load, and it explains webhook_url's purpose (completion callback) and the credit reservation tied to the number of emails. The emails array element format is left implicit, but it is self-evident from the name.

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 (queue/submit) plus the resource and mode (a list of emails for asynchronous verification). It is immediately distinguishable from the sibling verify_email (single, synchronous) and get_bulk_job (status polling).

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 routes the agent to get_bulk_job for status/results and flags webhook_url as the alternative completion mechanism. It does not, however, state when to prefer verify_email over this bulk path for a small list, so the when-not guidance is incomplete.

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