Verify B2B company registration numbers
Verify B2B company registration numbers, check trade register structure (UK Companies House, France SIREN/SIRET, Poland KRS, Germany Handelsregister, US DUNS/SOS), validate Luhn checksums, and infer legal entity structure
Request
- x-api-key: <your-api-key>
- Content-Type: application/json
Response
{
"companyDetails": {
"countryCode": "PL",
"entityType": "standard",
"expectedFormatExample": "<expected format example>",
"normalizedRegistrationNumber": "PL61109010140000071219812874",
"officialRegistryUrl": "https://example.com/page",
"rawInput": "PL61109010140000071219812874",
"registryAuthority": "<registry authority>"
},
"isValid": true,
"status": "success",
"tokensDeducted": 2,
"validationResult": {
"isChecksumValid": true,
"isFormatValid": true,
"jurisdictionDetected": "<jurisdiction detected>",
"reason": "checksum ok"
}
}What it does
Verify B2B company registration numbers, check trade register structure (UK Companies House, France SIREN/SIRET, Poland KRS, Germany Handelsregister, US DUNS/SOS), validate Luhn checksums, and infer legal entity structure
Request
Body
| Field | Type | Required | Description |
|---|---|---|---|
companyName | string | no | Optional company name for entity type classification and verification context. |
countryCode | string | no | Optional 2-letter ISO country code (e.g. "GB", "FR", "PL", "DE", "US"). Auto-detected if omitted. |
registrationNumber | string | yes | Trade registry identification number (e.g., "00059707", "732829320", "0000123456", "HRB 12345", or "1234567") |
Example request
{
"companyName": "Castomo P.S.A.",
"countryCode": "PL",
"registrationNumber": "<registration number>"
}Response
| Field | Type | Description |
|---|---|---|
companyDetails | object | |
↳ countryCode | string | |
↳ entityType | string | |
↳ expectedFormatExample | string | |
↳ normalizedRegistrationNumber | string | |
↳ officialRegistryUrl | string | |
↳ rawInput | string | |
↳ registryAuthority | string | |
isValid | boolean | |
status | string | |
tokensDeducted | integer | |
validationResult | object | |
↳ isChecksumValid | boolean | |
↳ isFormatValid | boolean | |
↳ jurisdictionDetected | string | |
↳ reason | string |
Example response
{
"companyDetails": {
"countryCode": "PL",
"entityType": "standard",
"expectedFormatExample": "<expected format example>",
"normalizedRegistrationNumber": "PL61109010140000071219812874",
"officialRegistryUrl": "https://example.com/page",
"rawInput": "PL61109010140000071219812874",
"registryAuthority": "<registry authority>"
},
"isValid": true,
"status": "success",
"tokensDeducted": 2,
"validationResult": {
"isChecksumValid": true,
"isFormatValid": true,
"jurisdictionDetected": "<jurisdiction detected>",
"reason": "checksum ok"
}
}Errors
Every error answers with the same envelope: an HTTP status, a machine code and a sentence.
400 | The body or a parameter failed validation. The details array names the field. |
401 | No key, a revoked key or a wrong header. Send x-api-key. |
402 | The wallet cannot cover this call. Top up or wait for the monthly grant. |
404 | The resource does not exist, or it is not yours. Both answer identically and cost nothing. |
429 | Over the per-minute quota of your tier. Back off and retry. |
5xx | Upstream refused or timed out. The call is not billed. |
Code
curl -X POST 'https://app.castomapi.com/v1/verify/company' \
-H 'x-api-key: <your-api-key>' \
-H 'Content-Type: application/json' \
-d '{"companyName": "Castomo P.S.A.", "countryCode": "PL", "registrationNumber": "<registration number>"}'const res = await fetch('https://app.castomapi.com/v1/verify/company', {
method: 'POST',
headers: { 'x-api-key': '<your-api-key>', 'Content-Type': 'application/json' },
body: JSON.stringify({"companyName": "Castomo P.S.A.", "countryCode": "PL", "registrationNumber": "<registration number>"})
});
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/company', {
method: 'POST',
headers: { 'x-api-key': '<your-api-key>', 'Content-Type': 'application/json' },
body: JSON.stringify({"companyName": "Castomo P.S.A.", "countryCode": "PL", "registrationNumber": "<registration number>"})
});
const data = await res.json();
console.log(data);import requests
res = requests.post(
'https://app.castomapi.com/v1/verify/company',
headers={'x-api-key': '<your-api-key>'},
json={"companyName": "Castomo P.S.A.", "countryCode": "PL", "registrationNumber": "<registration number>"},
timeout=30,
)
print(res.json())<?php
$ch = curl_init('https://app.castomapi.com/v1/verify/company');
curl_setopt_array($ch, [
CURLOPT_CUSTOMREQUEST => 'POST',
CURLOPT_RETURNTRANSFER => true,
CURLOPT_HTTPHEADER => ['x-api-key: <your-api-key>', 'Content-Type: application/json'],
CURLOPT_POSTFIELDS => json_encode(['companyName' => 'Castomo P.S.A.', 'countryCode' => 'PL', 'registrationNumber' => '<registration number>']),
]);
$data = json_decode(curl_exec($ch), true);
print_r($data);Cost and limits
This operation costs 2 tokens. A call that fails is never billed. Every account gets 1000 free tokens a month; paid balances never expire.
Rate limits per minute
| No key | 10 |
| Free | 60 |
| Pro | 300 |
| Enterprise | 1200 |
Questions
What does Verify B2B company registration numbers cost?
2 tokens per successful call, debited from your wallet after the response. Failed calls are free. Every account receives 1000 free tokens a month.
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