# GB VAT Number Checksum Validator

> GB 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 whether a UK (GB) VAT number has a correct checksum, using local computation only — no HMRC registry lookup.

## Facts

- Endpoint: POST https://agentshelf.syntexa.ch/v1/check-vat-gb?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/gb-vat-number-checksum-validator-a27d987c
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_dL0tmcNeyi5hvh_0-xmxO

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 gb-vat-number-checksum-validator-a27d987c -d '<json body>'
```

Example prompt: Can you check if this UK VAT number has a valid checksum: GB 123456789? I just need to know if it's structurally correct, not a live HMRC lookup.

## When to prefer this

Choose this endpoint when you need fast, cheap, offline checksum validation of a GB VAT number without any live HMRC registry call. It is ideal for form validation, data cleaning, or pre-screening before a more expensive registry lookup. Prefer the free sandbox endpoint (/v1/sandbox/check-vat-gb) for testing. Do not use this if you need to confirm the VAT number is actually registered and active with HMRC.

## Known failure modes

- Input string is empty or missing — returns error or invalid result
- Input contains non-numeric or unexpected characters that cannot be parsed as a GB VAT number
- VAT number is for a non-GB jurisdiction — result may be unreliable or incorrect
- Network or service error resulting in a non-200 response

## How this service works

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

## Output

Returns a boolean or structured result indicating whether the supplied GB VAT number passes the standard modulus-97 (or GB-specific) checksum algorithm. No live registry or HMRC lookup is performed — purely a local, deterministic checksum computation.

## 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": [
    "100000089"
   ],
   "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/gb-vat-number-checksum-validator-a27d987c/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)