Verify a single email's deliverability (syntax, DNS/MX, SMTP mailbox, disposable / role / catch-all detection, confidence score).
Costs 1 credit for a billable result (valid/invalid/catch_all/disposable/do_not_mail),
whether fresh or served from cache. `unknown` results are free. Requires an
API key. Returns {success, credits_used, result}.
| Name | Required | Description | Default |
|---|---|---|---|
| Yes |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Goes well beyond the annotations (readOnlyHint=false, openWorldHint=true) by disclosing the billing model, the exact set of billable outcomes, that `unknown` is free, the API-key prerequisite, and the return envelope. An agent knows the cost and side effects before calling, which is exactly the burden the annotations leave open.
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?
Front-loads the purpose in one sentence, then adds only the three things an agent cannot infer: cost, auth requirement, and return shape. No filler, and the parenthetical check list is dense but immediately useful.
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 supplies the return envelope and billing semantics, and the single parameter needs little explanation. Gaps are minor: no mention of error/failure behavior when the API key is missing or invalid, and no rate-limit context for a metered external call.
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 0% and the single parameter has no description, but the parameter is one self-evident string named `email` and the description confirms the tool takes one email address. No format, normalization, or delimiter guidance is added, so it is adequate but not compensating much.
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+resource (verify an email's deliverability) and enumerates the checks performed (syntax, DNS/MX, SMTP, disposable/role/catch-all, confidence). The word 'single' scopes it against the bulk sibling, but it never names verify_email_demo or submit_bulk_verification, so the sibling distinction is inferential rather than explicit.
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?
Gives cost and auth context (1 credit for billable results, free `unknown`, requires an API key) that shapes when it is worth calling, but offers no explicit routing guidance such as using verify_email_demo for testing or submit_bulk_verification for lists. Usage is implied by cost economics rather than stated.
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.