Validate an email address against RFC 5322 syntax before storing it, sending a transactional email, or adding it to a mailing list. Returns { valid, email } — use this to avoid bounces and malformed data.
| Name | Required | Description | Default |
|---|---|---|---|
| Yes | Email address to validate |
| Name | Required | Description | Default |
|---|---|---|---|
| No | |||
| valid | No | ||
| reason | No |
Changes observed during successful MCP inspections.
Input schema / examplesAdded value: +[
+ {
+ "email": "john.doe@example.com"
+ }
+]Output schema / properties / reasonAdded value: +{
+ "type": "string"
+}Output schema / propertiesAdded value: +{
+ "email": {},
+ "valid": {
+ "type": "boolean"
+ }
+}Output schema / (root)Previous value: -nullNew value: +{
+ "additionalProperties": true,
+ "type": "object"
+}Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, idempotentHint, and non-destructive behavior, so the description only needs to add context beyond that, and it does: the RFC 5322 scope implies a pure syntax check with no network/MX lookup. The 'avoid bounces' claim slightly oversells a format check, keeping it at 4 rather than 5.
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?
Two front-loaded sentences with the action first and the use cases after. The 'Returns { valid, email }' fragment partially duplicates the existing output schema, which is the only wasted space.
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, the single parameter is fully documented in schema, annotations cover the safety profile, and an output schema exists, so return values need no explanation. Nothing an agent needs in order to call this correctly 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 coverage is 100% for the single 'email' parameter, so the baseline is 3, and the description earns one more by qualifying the validation rule as RFC 5322 syntax, which adds meaning beyond the schema's 'Email address to validate'. No format examples or edge cases (e.g., internationalized addresses) are given.
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 and resource ('Validate an email address') and narrows the standard to RFC 5322 syntax, which tells an agent exactly what kind of validation this is. No sibling tool in the list overlaps with email validation, so the purpose is unambiguous in the catalog.
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 three concrete trigger contexts: before storing, sending a transactional email, or adding to a mailing list. It does not name an alternative tool or any when-not condition (e.g., that this is format-only and not a deliverability check), so it stops short of a 5.
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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