verify_emailsCheck up to ten email addresses for deliverability by querying receiving mail servers, returning valid or invalid without sending messages.
Checks whether email addresses can receive mail by asking the receiving mail server, without sending a message. Returns valid or invalid for each address. Can take up to a minute.
| Name | Required | Description | Default |
|---|---|---|---|
| emails | Yes | The addresses to check, at most ten. |
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations declare readOnlyHint=false, openWorldHint=true, and idempotentHint=false, so the agent already knows this performs an external, non-idempotent operation. The description adds valuable context: no message is sent, results can take up to a minute, and output is valid/invalid per address. It doesn't mention rate limits, authentication, or failure modes, but it meaningfully extends the annotated behavior.
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?
Three tight sentences: what it does, what it returns, and the latency caveat. The latency warning is front-loaded enough to set expectations and nothing is wasted.
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 single-parameter tool with no output schema and full annotation coverage, the description covers mechanism, return values, and latency. It does not explain error handling (e.g., what happens for malformed addresses) or the distinction from check_email_domain, so it is not fully complete.
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% and the schema itself documents the emails array and its ten-address cap. The description adds no per-parameter syntax, format, or validation detail beyond what the schema already provides, so the baseline of 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 (checks/verify) and resource (email addresses) and clarifies the mechanism: querying the receiving mail server without sending a message. It could be confused with the sibling check_email_domain, which validates domains rather than individual addresses, but the description does not distinguish between them.
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 by the purpose but there is no explicit when-to-use guidance, no mention of alternatives like check_email_domain, and no prerequisites stated. An agent can infer the context but must reason about it.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.