Check Northern Ireland VAT numbers
Validate Northern Ireland VAT numbers (XI prefix) against the EU VIES registry. The Windsor Framework gives XI numbers VIES eligibility for goods trade with the EU, separate from the GB numbers used for services. vatverify routes XI lookups to the EU Commission VIES endpoint and returns the company name, address, and validity at query time.
Try it
curl -X POST "https://api.vatverify.dev/v1/validate" \ -H "Authorization: Bearer $VATVERIFY_KEY" \ -H "Content-Type: application/json" \ -d '{"vat_number":"XI174918972"}'Facts
Format
- Prefix
- XI
- Digits
- 9
- Regex
- ^XI\d{9}$
XI174918972XI174918970XI17491897VAT rates (GBP)
What we return for Northern Ireland
{
"data": {
"valid": true, // boolean validity at query time
"vat_number": "DE129273398",
"country": {
"code": "DE",
"name": "Germany",
"vat": { "standard_rate": 19 }
},
"company": {
"name": "SIEMENS AG", // legal entity name
"address": "..." // when VIES provides it
},
"verified_at": "2026-04-25T10:00:00Z"
},
"meta": {
"request_id": "019dc...", // for audit trail correlation
"source": "vies",
"source_status": "live", // live | cached | degraded
"cached": false,
"latency_ms": 234
}
}
Watch out for
- XI prefix is real: post-Brexit protocol issues Northern Ireland businesses VIES-eligible numbers separately from GB.
- XI numbers cover goods only (not services) per the Windsor Framework; EU reverse-charge rules apply for goods, normal GB rules for services.
- XI format looks like VIES but routes through the EU Commission's VIES endpoint, not HMRC.
XI is a post-Brexit compromise
The Windsor Framework (originally the Northern Ireland Protocol) created an odd category: Northern Ireland businesses that trade goods with the EU need VIES-eligible VAT numbers, because those trades follow EU customs rules. But services in Northern Ireland stay under UK VAT rules.
The compromise: Northern Ireland businesses get both identifiers.
- GB-prefix number: used for services and UK-domestic trade.
- XI-prefix number: used for EU goods trade; appears in VIES.
The XI prefix looks like a typo but it's intentional: a distinct ISO-3166 code was needed because GB is now entirely outside VIES, and Northern Ireland goods trade needed a VIES-visible identifier without reopening GB in VIES.
Validation routing
XI numbers route through VIES (the EU Commission endpoint), not HMRC. Our
/v1/validate handles the routing automatically. Callers pass an XI number
and get back the same response shape as any other VIES-covered country.
The 9-digit format matches GB-prefix numbers structurally because they're
often the same business with a different prefix. A single Belfast company
may have both GB123456789 (for services) and XI123456789 (for goods
exports). Both are valid, return different responses, and neither is a
duplicate of the other.
Practical implication for accounting systems
Invoicing systems built before 2021 typically store a single VAT number per customer. Northern Ireland customers break that assumption; you may need to invoice the same legal entity under either prefix depending on what you are selling.
A storage shape that holds up:
- Add a second VAT field on the customer record (for example
vat_xi) alongside the existingvat_number. - For each line item, pick the prefix based on the goods-or-services flag.
- Validate both numbers on customer creation. Flag a warning if you have only one for an NI-domiciled customer, since most NI businesses trading B2B with the EU will have both.
When to check XI vs GB
A short heuristic:
- Invoice for services to a Northern Ireland business: validate the GB number. UK VAT rules apply.
- Invoice for goods from an EU member state to a Northern Ireland business: validate the XI number. EU reverse-charge applies.
If a Northern Ireland counterparty gives you only a GB number and you are invoicing goods, ask for the XI equivalent. They will have one if they trade goods cross-border.
EU reverse-charge eligibility for XI
For an EU seller making a B2B intra-Community supply of goods to a Northern Ireland customer, the XI number is what triggers the zero-rate / reverse-charge mechanism. The legal basis sits in EU VAT Directive Article 138 just as it does for any EU-internal supply.
You cannot use the customer's GB number for this purpose. The EU treats GB-prefix numbers as third-country, and the supply would fall back to the customer's destination rules with import VAT implications. An audit that finds a goods supply zero-rated against a GB number will be challenged.
When XI numbers go invalid
Northern Ireland businesses that stop trading goods with the EU can let
their XI registration lapse. The number will return valid: false from
VIES while the matching GB number still validates from HMRC. If you see
this pattern on a previously-valid customer, ask before invoicing the
next goods shipment. You may be the first to notice the change.
Automate Northern Ireland VAT checks in your stack
Replace manual lookups with one API call against VIES. Drops into invoicing, checkout, and signup flows in any language. 500 free validations per month, no credit card.