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POST /v1/verify/regon free No key needed Verify

Validate Polish NIP (Tax Identification Number) (POST regon)

Validate Polish NIP (Tax Identification Number) and REGON (Business Registry Number) mathematical Modulo 11 checksums

POST

Request

  • x-api-key: <your-api-key>
  • Content-Type: application/json

Response 

{
  "isValid": true,
  "nipResult": {
    "isValid": true,
    "normalized": "PL61109010140000071219812874",
    "rawInput": "PL61109010140000071219812874",
    "reason": "checksum ok"
  },
  "regonResult": {
    "isValid": true,
    "normalized": "PL61109010140000071219812874",
    "rawInput": "PL61109010140000071219812874",
    "reason": "checksum ok",
    "type": "standard"
  },
  "status": "success",
  "tokensDeducted": 1
}
The response below is a mock built from the endpoint's own schema — no request leaves this page. Edit the body, press Send, read the shape you will get back. Run it for real in the dashboard →

What it does

Validate Polish NIP (Tax Identification Number) and REGON (Business Registry Number) mathematical Modulo 11 checksums

Request

Body

FieldTypeRequiredDescription
identifierstringnoAuto-detected fallback identifier (will auto-detect NIP or REGON based on length)
nipstringnoPolish NIP taxpayer identification number (e.g. "5252604877" or "525-260-48-77")
regonstringnoPolish REGON business entity number (9 or 14 digits)

Example request

{
  "identifier": "<identifier>",
  "nip": "8993033031",
  "regon": "542471636"
}

Response

FieldTypeDescription
isValidboolean
nipResultobject
  ↳ isValidboolean
  ↳ normalizedstring
  ↳ rawInputstring
  ↳ reasonstring
regonResultobject
  ↳ isValidboolean
  ↳ normalizedstring
  ↳ rawInputstring
  ↳ reasonstring
  ↳ typestring
statusstring
tokensDeductedinteger

Example response

{
  "isValid": true,
  "nipResult": {
    "isValid": true,
    "normalized": "PL61109010140000071219812874",
    "rawInput": "PL61109010140000071219812874",
    "reason": "checksum ok"
  },
  "regonResult": {
    "isValid": true,
    "normalized": "PL61109010140000071219812874",
    "rawInput": "PL61109010140000071219812874",
    "reason": "checksum ok",
    "type": "standard"
  },
  "status": "success",
  "tokensDeducted": 1
}

Errors

Every error answers with the same envelope: an HTTP status, a machine code and a sentence.

400The body or a parameter failed validation. The details array names the field.
401No key, a revoked key or a wrong header. Send x-api-key.
402The wallet cannot cover this call. Top up or wait for the monthly grant.
404The resource does not exist, or it is not yours. Both answer identically and cost nothing.
429Over the per-minute quota of your tier. Back off and retry.
5xxUpstream refused or timed out. The call is not billed.

Code

curl -X POST 'https://app.castomapi.com/v1/verify/regon' \
  -H 'x-api-key: <your-api-key>' \
  -H 'Content-Type: application/json' \
  -d '{"identifier": "<identifier>", "nip": "8993033031", "regon": "542471636"}'
const res = await fetch('https://app.castomapi.com/v1/verify/regon', {
  method: 'POST',
  headers: { 'x-api-key': '<your-api-key>', 'Content-Type': 'application/json' },
  body: JSON.stringify({"identifier": "<identifier>", "nip": "8993033031", "regon": "542471636"})
});
const data = await res.json();
console.log(data);
import { request } from 'node:https';

// Node 18+ has fetch built in
const res = await fetch('https://app.castomapi.com/v1/verify/regon', {
  method: 'POST',
  headers: { 'x-api-key': '<your-api-key>', 'Content-Type': 'application/json' },
  body: JSON.stringify({"identifier": "<identifier>", "nip": "8993033031", "regon": "542471636"})
});
const data = await res.json();
console.log(data);
import requests

res = requests.post(
    'https://app.castomapi.com/v1/verify/regon',
    headers={'x-api-key': '<your-api-key>'},
    json={"identifier": "<identifier>", "nip": "8993033031", "regon": "542471636"},
    timeout=30,
)
print(res.json())
<?php
$ch = curl_init('https://app.castomapi.com/v1/verify/regon');
curl_setopt_array($ch, [
    CURLOPT_CUSTOMREQUEST => 'POST',
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_HTTPHEADER => ['x-api-key: <your-api-key>', 'Content-Type: application/json'],
    CURLOPT_POSTFIELDS => json_encode(['identifier' => '<identifier>', 'nip' => '8993033031', 'regon' => '542471636']),
]);
$data = json_decode(curl_exec($ch), true);
print_r($data);

Cost and limits

This operation needs no API key and costs nothing: called without a key it answers 200 and deducts zero tokens, up to 10 requests a minute per IP address.

Rate limits per minute

No key10
Free60
Pro300
Enterprise1200

Docs → Pricing

Questions

What does Validate Polish NIP (Tax Identification Number) (POST regon) cost?

This operation needs no API key and costs nothing: called without a key it answers 200 and deducts zero tokens, up to 10 requests a minute per IP address.

How do I authenticate?

Send your key in the x-api-key header. One key covers every metered endpoint; there is nothing to enable per endpoint.

Can I send an Authorization: Bearer token instead?

Not for a metered endpoint — those take the x-api-key header and nothing else. Bearer tokens belong to the account side: the dashboard and account APIs accept a JWT session, and castomapi-auth issues those through a standard OAuth2 handshake, with authorization code, client credentials and refresh grants. The auth service page covers it.

What are the limits?

10 requests a minute per IP with no key at all, 60 a minute on the free tier, 300 on Pro, 1200 on Enterprise. Above the no-key tier the quota is per account, across every endpoint.

OpenAPI: https://app.castomapi.com/docs/json