VAT ID Validator

The official way to check an EU VAT number is VIES, and VIES has two habits that cost time: it is rate-limited, and whole member states drop out of it for hours. What VIES never tells you is whether a number is even structurally possible. This validator answers exactly that, offline: country format plus the national check digit algorithm, for one ID or a whole customer list, with the reason spelled out for every failure.

What this validator checks

Every number goes through the same three stages, and the report always names the stage it reached, because the honest answer to "is this VAT ID valid" has three parts:

1. Format. Each country has an exact shape: DE takes 9 digits and the first is never 0, ATU takes the letter U and 8 digits, NL takes 9 digits, a B and 2 more. A number that fails here is wrong no matter what any registry says, and the report tells you how it misses, for example "Austria expects ATU followed by 8 digits, this has 7 digits after the U".
2. Check digits. Nearly every country bakes a checksum into the number. Where the algorithm is public, it runs here: ISO 7064 MOD 11,10 for Germany and Croatia, Luhn for Italy and Sweden, mod 97 for Belgium, mod 89 for Luxembourg, weighted sums elsewhere. A handful of number types have no reliable public rule, and the report says so instead of pretending: French keys with letters, Czech and Latvian personal numbers, the Spanish K/L/M series. Those get a "format verified" badge, never a fake pass.
3. Registration. This stage is named but deliberately not performed. Whether a structurally valid number is assigned and active right now, only the registry knows, and that means VIES, or HMRC for GB, or the Swiss UID register. No offline tool can answer it, including this one, and any tool implying otherwise is overselling.

Before stage 1, each line is normalized: spaces, dots, dashes and case are ignored, GR becomes the EL prefix Greece actually uses, a doubled prefix loses one copy, a missing U after AT is inserted, a 9-digit legacy Belgian number gets its leading 0. Every repair is listed in the notes so the exported report shows what should be fixed in the source data. Two options round it off: --guess-country takes a line pasted without its prefix, tests it against every country and names the unique match if there is one, and --duplicates flags lines that normalize to the same ID.

Anatomy of a VAT number

An EU VAT ID is a two-letter country prefix plus a national number. The prefix follows ISO 3166 with two exceptions worth knowing: Greece uses EL instead of GR, and Northern Ireland uses XI, a code invented for the Brexit protocol. Switzerland is outside the system entirely and writes its number as CHE-123.456.789 MWST.

The national part is rarely a number invented just for VAT. Most countries reuse their company register: a French VAT ID is a 2-digit key in front of the SIREN, a Swedish one is the organisationsnummer with 01 appended, a Danish one is the CVR number, a Czech one the IČO. That is why the shapes differ so much, from Romania's 2 digits minimum to Lithuania's 12, and why the check digit algorithms are national inventions rather than one EU scheme. It also means a VAT ID often leaks a little structure: the Dutch B01 suffix counts establishments, the Swedish tail is a group number, and an Austrian UID always starts with U.

Formats by country

The structure column describes what follows the prefix. "Check digits" says whether this tool verifies the checksum or, where no public rule exists for a number type, checks the format only.

What VIES can and cannot do

VIES is not a database. It is a relay: the Commission forwards your query to the member state that issued the number, and returns whatever that national system answers. That design explains all three of its famous behaviours.

First, MS_UNAVAILABLE. When a national database is down for maintenance, every query for that country fails while the other 26 keep working. Anyone who has run batch validations has watched one country vanish for an evening. Second, throttling: the service answers a request at a time per consumer and returns MS_MAX_CONCURRENT_REQ or GLOBAL_MAX_CONCURRENT_REQ when a script hammers it, so a naive loop over 2,000 debtors is exactly the workload it dislikes. Third, no memory: VIES answers for the moment of the query. It cannot tell you whether a number was valid last March when the invoice was written, which is why the consultation number you get for a confirmed query (you must state your own VAT ID to receive one) is worth storing, it is the only evidence of that moment you will ever have.

What VIES does not check at all is structure in any helpful way: a mistyped number simply comes back "invalid", the same word you would get for a real but deregistered one. It will not tell you that your Austrian number has seven digits instead of eight. That gap between "invalid" and "why" is the part this tool covers.

Syntax check vs. registration check

The two checks are routinely confused, including by tools that call a format regex a "VAT validation". They answer different questions and fail in different directions.

The syntax check, format plus check digits, is pure arithmetic and needs no network. Its strength is the direction of certainty: a failure is final. If the ISO 7064 check digit of a German number computes to 6 and the number ends in 9, no registry lookup can save it; someone mistyped it, and the report can even say which kind of slip is plausible. Check digit schemes are designed for exactly these accidents: every single-digit error is caught by all the schemes in the table, and most adjacent transpositions too. In a fresh debtor export, nearly every bad ID is this kind of bad, which is why the offline stage catches the bulk of the problems before a single request is spent.

The registration check has the opposite asymmetry. A VIES "valid" is authoritative for that moment. A VIES "invalid" is ambiguous: typo, deregistration, a freshly issued ID not yet synced, or a national outage misreported by an impatient client. Running syntax first splits those cases cleanly: structurally broken numbers never reach the lookup, and a structurally sound number that VIES rejects is a genuinely interesting case worth a human look, not a retry loop.

Treat the two stages as a funnel with an audit trail. Offline check on every save in the ERP, VIES on onboarding and before zero-rated invoice runs, consultation number into the customer record. Cheap, and each stage does the one thing it is actually able to do.

Reverse charge and the customer's ID

The reason businesses care about any of this is the zero-rating of intra-EU B2B supplies. Deliver goods from Vienna to a company in Hamburg, invoice without Austrian VAT, and the customer self-accounts for German VAT: that construction stands on the customer having a valid VAT ID at the time of supply. Since the 2020 quick fixes amended Article 138 of the VAT Directive, that ID is a substantive condition, not a formality; if it turns out invalid and the supplier cannot show a reasonable verification effort, the supplier owes the VAT plus interest, years later, at the audit.

Honesty about what that means for this tool: an offline pass is not the verification the auditor wants. The proof that counts is the registry confirmation, ideally VIES queried with your own ID stated so a consultation number comes back, stored with a date. The offline check earns its place one step earlier, by making sure the ID you send to VIES, print on the invoice and key into the ERP is at least a number that can exist. A transposed digit found at audit time is expensive; found at data entry it is a red row in a report.

Preflighting a debtor list

The batch mode exists for one recurring situation: a customer master export is about to be imported, migrated or cleaned, and somewhere in those rows are the IDs typed by hand five years ago. Paste the column, one ID per line, up to 5,000 lines. Lines with ; or tab separators are treated as CSV rows and only the first column is read, so a quick copy out of a spreadsheet works without reshaping.

The report is written to be forwarded: every line gets a verdict with the country spelled out, the exact failure reason where there is one, and a notes section listing every repair the normalizer made, every country it had to guess and every duplicate, with line numbers. The stats row on the panel gives the four numbers a migration ticket needs: checked, passed, format-only, failed. Copy or download the whole thing as text. The same export usually has an IBAN column sitting next to the VAT IDs; the IBAN validator runs the equivalent preflight on that one.

And because a debtor list is customer data: the list never leaves this tab. There is no server-side validation step, no VIES call in the background, no logging of what you paste, and the page works the same with the network tab open, which is the check we would run on any online tool before pasting business data into it.

Two algorithms, worked through

Check digit schemes sound more mysterious than they are, so here are the two you are most likely to need by hand, on real structurally valid numbers.

Austria: ATU13585627

Take the 7 digits after the U: 1 3 5 8 5 6 2. Weight them 1, 2, 1, 2, 1, 2, 1 and reduce two-digit products to their digit sum: 1, 6, 5, 16→7, 5, 12→3, 2. The total is 29. The check digit is (96 − 29) mod 10 = 7, and the number ends in 7, so it passes. Change any single digit and the total shifts, which is the entire point of the construction.

Germany: DE136695976

ISO 7064 MOD 11,10 is a running product rather than a weighted sum. Start with product 10; for each of the first eight digits, add it to the product, take mod 10 (a result of 0 becomes 10), double, take mod 11:

The check digit is 11 minus the final product: 11 − 5 = 6, and the number ends in 6. The scheme catches every single-digit error and every adjacent transposition, which a plain digit sum cannot claim, and that is why Germany and Croatia picked it.

The other 25 countries are variations on these ideas with different weights and moduli; the table above names each one. If a number of yours fails and you want to see the arithmetic, the report quotes both the computed and the actual digit, so recomputing by hand takes a minute.

VAT number questions