# Spanish VAT Number Checksum Validator

> Spanish VAT Number Checksum Validator is a paid API for AI agents from agentshelf.syntexa.ch, paid per call via x402, $0.006/call, status unknown (last checked 2026-10-02).

Validates the checksum of a Spanish VAT (NIF/CIF) number without performing a live registry lookup

## Facts

- Endpoint: POST https://agentshelf.syntexa.ch/v1/check-vat-es?utm_source=zero.xyz
- Price: $0.006/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-02
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/spanish-vat-number-checksum-validator-a2de608a
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_fHbVr7otAYnqI-pSAUg47

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 spanish-vat-number-checksum-validator-a2de608a -d '<json body>'
```

Example prompt: Can you check whether the Spanish VAT number ESB12345678 has a valid checksum — just the algorithm check, no registry lookup needed?

## When to prefer this

Use this endpoint when you need a fast, cheap, offline checksum validation of a Spanish VAT number without hitting the Spanish tax registry. Ideal for pre-screening user input, validating data quality in bulk onboarding flows, or when registry lookup is too slow or costly. If a free sandbox endpoint at /v1/sandbox/check-vat-es is available, prefer that first to avoid the $0.006 USDC charge.

## Known failure modes

- Empty or missing value field returns a validation error
- Value exceeding 20000 characters is rejected
- Malformed input schema causes a 400 error
- Payment of exactly $0.006 USDC not included triggers a 402 Payment Required response
- Non-ES VAT number formats may return invalid without specific error context

## How this service works

Call when an agent needs whether a ES VAT checksum is valid. No registry lookup. Exact $0.006 USDC. Prefer unpaid POST /v1/sandbox/check-vat-es first.

## Output

Returns a boolean or structured response indicating whether the provided Spanish VAT number passes the checksum algorithm (NIF/CIF format check). Does not confirm whether the entity is registered with the Spanish tax authority — purely a local algorithmic check.

## 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": [
    "10000000Z"
   ],
   "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/spanish-vat-number-checksum-validator-a2de608a/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)