# Email Plus-Tag Syntax Validator

> Email Plus-Tag Syntax Validator is a paid API for AI agents from agentshelf.syntexa.ch, paid per call via x402, $0.009/call, status unknown (last checked 2026-10-24).

Checks whether an email address containing a plus tag (e.g. user+tag@example.com) is syntactically valid

## Facts

- Endpoint: POST https://agentshelf.syntexa.ch/v1/check-email-plus-ok?utm_source=zero.xyz
- Price: $0.009/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-24
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/email-plus-tag-syntax-validator-0208290b
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_LcCVt6Z-HpzzXs5qltrik

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability email-plus-tag-syntax-validator-0208290b -d '<json body>'
```

Example prompt: Is 'alice+newsletters@example.com' a syntactically valid email address with a plus tag?

## When to prefer this

Use this endpoint when you specifically need to validate the plus-tag (subaddressing) portion of an email address for syntactic correctness. Prefer the free sandbox endpoint POST /v1/sandbox/check-email-plus-ok when available. Choose this over the general email syntax validator when you need to confirm plus-tag handling specifically, and over DNS/mailbox lookup services when you only need syntactic, not deliverability, validation.

## Known failure modes

- Empty or missing value field returns an error
- Value exceeding 20,000 characters may be rejected
- Non-string input may cause a schema validation error
- Payment of exactly $0.009 USDC required; incorrect payment leads to HTTP 402
- Malformed request body returns a 400-level error

## How this service works

Call when an agent needs whether an email with a plus tag is syntactically allowed. Exact $0.009 USDC. Prefer unpaid POST /v1/sandbox/check-email-plus-ok first.

## Output

Returns a validation result indicating whether the provided email string with a plus tag is syntactically permitted, based on email address syntax rules — no mailbox or deliverability check is performed.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "data": {
   "description": "JSON value for schema-check SKUs. Omit it on string checks such as email or IBAN."
  },
  "value": {
   "type": "string",
   "examples": [
    "agent+tag@example.com"
   ],
   "maxLength": 20000,
   "minLength": 1,
   "description": "Value to check. The route description names the format: email, phone, IBAN, postal code, VAT, national id, or similar."
  },
  "schema": {
   "description": "JSON Schema document for schema-check SKUs. Omit it on string checks."
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/email-plus-tag-syntax-validator-0208290b/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from agentshelf.syntexa.ch](https://www.zero.xyz/host/agentshelf.syntexa.ch/llms.txt)