Syntax, MX and deliverability check for an email.
Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.
{
"id": 1,
"jsonrpc": "2.0",
"method": "tools/call",
"params": {
"arguments": {
"email": "<email>"
},
"name": "email_verify"
}
}| Name | Required | Description | Default |
|---|---|---|---|
| Yes | Email address to verify |
Changes observed during successful MCP inspections.
Input schema / properties / emailAdded value: +{
+ "description": "Email address to verify",
+ "type": "string"
+}Input schema / requiredAdded value: +[
+ "email"
+]Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden, and it does disclose the internal checks performed, which is real behavioral content. However, it is silent on whether this is a live SMTP/network probe or a heuristic, whether it consumes rate-limited quota, and what a 'deliverability' result actually means, which matters for an external-domain lookup.
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?
One front-loaded sentence with zero filler and no redundancy. It is efficient nearly to the point of terseness, leaving no room for qualifying language about scope.
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?
The tool is simple (one required string, no nested objects), but there is no output schema, so the description should indicate the shape of the result (boolean, verdict enum, or detailed diagnostic) and does not. It is adequate but leaves an agent guessing at the return value and at whether the check is live.
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?
There is a single required parameter and schema description coverage is 100%, so the schema already documents 'email' adequately. The description adds no format, normalization, or domain-requirement guidance, 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?
The description names a specific resource (email) and enumerates the three checks performed (syntax, MX, deliverability), which is far more informative than the tool name alone. It does not explicitly contrast with any sibling, but no sibling in the list performs email validation, so disambiguation is implicit.
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?
There is no statement of when to use this versus alternatives (e.g., iban_validate, ipv4_validate, or plain regex), and no mention of prerequisites such as requiring a domain to be resolvable. Usage is only inferable from the name and check list.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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