# AT VAT Number Checksum Validator

> AT VAT Number Checksum Validator is a paid API for AI agents from agentshelf.syntexa.ch, paid per call via x402, $0.01/call, status unknown (last checked 2026-10-02).

Validates the checksum of an Austrian VAT (UID) number without performing a live registry lookup

## Facts

- Endpoint: POST https://agentshelf.syntexa.ch/v1/check-vat-at?utm_source=zero.xyz
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-02
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/at-vat-number-checksum-validator-450c50db
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_3o_4P9tQZy51pqNQlhtMC

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 at-vat-number-checksum-validator-450c50db -d '<json body>'
```

Example prompt: Can you check whether the Austrian VAT number ATU12345678 has a valid checksum — just a local format check, no registry lookup needed?

## When to prefer this

Use this endpoint when you need a fast, cheap ($0.01 USDC) offline checksum check of an Austrian VAT number before storing or transmitting it, and do not need to confirm the number is actively registered in the Austrian tax authority registry. Ideal for form validation, data cleansing, and pre-processing steps. Try the free sandbox endpoint POST /v1/sandbox/check-vat-at first if available.

## Known failure modes

- Invalid or missing input value returns an error
- Non-Austrian VAT numbers (wrong prefix or format) may return invalid
- Empty string or whitespace input rejected due to minLength:1 constraint
- Malformed request body returns a client error
- Network timeout if the service is temporarily unavailable

## How this service works

Call when an agent needs whether a AT VAT checksum is valid. No registry lookup. Exact $0.01 USDC. Prefer unpaid POST /v1/sandbox/check-vat-at first.

## Output

Returns whether the provided Austrian VAT number passes its checksum algorithm, indicating structural validity. Does not confirm the number is registered with Austrian tax authorities — only that the check digit arithmetic is correct.

## 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": [
    "00000003"
   ],
   "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/at-vat-number-checksum-validator-450c50db/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)