verify_emailCheck whether an email address exists and is safe to send to, with a real SMTP handshake. Free. Returns valid, invalid, catchall, disposable or unknown. For more than a handful of addresses put them in a list and use verify_list_start instead.
| Name | Required | Description | Default |
|---|---|---|---|
| Yes | Address to verify |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, and non-destructive hints; the description adds the real SMTP handshake method and the exact classification output (valid, invalid, catchall, disposable, unknown). It also notes the tool is free, which is useful operational context beyond what annotations provide.
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 sentences with no wasted words. The core purpose is front-loaded, the output categories are stated briefly, and the sibling alternative is provided compactly.
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 covers the return values, the verification method, cost, and the batching alternative. For a single-parameter, read-only tool, this is everything an agent needs to invoke it correctly.
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 single parameter is clearly described as 'Address to verify.' The description reinforces that the address is an email address but adds no format or syntax detail beyond the schema, so a baseline score is appropriate.
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 ('Check') and resource ('an email address'), and defines the exact scope: whether it exists and is safe to send to. It distinguishes itself from verify_list_start by explicitly noting the single-address use case, and the SMTP handshake detail sets it apart from more generic lookups.
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?
It explicitly states when to switch to an alternative: 'For more than a handful of addresses put them in a list and use verify_list_start instead.' This gives an agent a clear decision rule for choosing this tool versus the batch sibling.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Add one secure layer between your agents and this server.