# Austrian Firmenbuchnummer (FN) Validator

> Austrian Firmenbuchnummer (FN) Validator is a paid API for AI agents from toll402.dev, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-14).

Validates and verifies an Austrian Firmenbuchnummer (company register number) by computing and comparing its modulo-11 check letter offline.

## Facts

- Endpoint: POST https://toll402.dev/v1/t/fn_at_validate
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/austrian-firmenbuchnummer-fn-validator-bf2f0ebb
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_ym1kz-1DeZtVwNrOW3mQE

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 austrian-firmenbuchnummer-fn-validator-bf2f0ebb -d '<json body>'
```

Example prompt: Can you check if 'FN 123456k' is a valid Austrian Firmenbuchnummer — just confirm whether the check letter is correct?

## When to prefer this

Use this endpoint when you need a fast, cheap, offline structural check of an Austrian Firmenbuchnummer — ideal for form validation, KYB pipelines, or data quality audits where you don't need a live registry lookup, just a check-digit verification.

## Known failure modes

- Invalid or missing 'value' field returns an error response
- FN number with non-numeric body or unsupported format may fail to parse
- Check letter not in the expected letter table (p,a,b,c,d,e,f,g,h,i,k) causes validation failure
- Network or payment (x402) issues may prevent the call from completing

## How this service works

Offline validator for an Austrian Firmenbuchnummer (FN), the company register number. Normalizes the numeric part (1-6 digits, left-padded to 6 for calculation), computes the modulo-11 check letter using weights 2,1,2,1,2,1 (Luhn-style digit reduction for products >=9 by subtracting 9) and the standard letter table (0=p,1=a,2=b,3=c,4=d,5=e,6=f,7=g,8=h,9=i,10=k), and compares it to the supplied check letter.

## Output

A validation response indicating whether the supplied Austrian Firmenbuchnummer has a correct modulo-11 check letter, based on offline computation without any external registry lookup.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method",
    "bodyType",
    "body"
   ],
   "properties": {
    "body": {
     "type": "object",
     "required": [
      "value"
     ],
     "properties": {
      "value": {
       "type": "string",
       "description": "Firmenbuchnummer, e.g. 'FN 123456k' or '123456k'"
      }
     },
     "additionalProperties": false
    },
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "POST"
     ],
     "type": "string"
    },
    "bodyType": {
     "enum": [
      "json",
      "form-data",
      "text"
     ],
     "type": "string"
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/austrian-firmenbuchnummer-fn-validator-bf2f0ebb/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from toll402.dev](https://www.zero.xyz/host/toll402.dev/llms.txt)