Checking a VAT number
You can check any VAT number issued anywhere in the European Union, free, at the Commission’s VIES service.
It is quick and it is worth doing when an invoice charges you VAT. It is also more limited than most people assume.
What a valid result means
VIES tells you that the number is currently valid in the issuing member state’s own database. Where that member state chooses to release it, you will also get the registered name and address attached to the number.
That last part is not guaranteed. Some member states withhold the name and address, so VIES can confirm a number is real without confirming whose it is. If you need to tie the number to the business in front of you and VIES will not show you a name, that check has not actually completed.
VIES is a query engine, not a database
This matters when it fails. VIES does not hold a copy of anything. It passes your query to the tax authority of the country that issued the number and relays the answer.
So a service unavailable message means that country’s system is not responding. It does not mean the number is invalid. Try again later rather than concluding anything.
No VAT number is usually not a problem
This is the part worth internalising, because it causes needless suspicion.
A business only has to register for VAT once it passes the turnover thresholds. Plenty of entirely legitimate sole traders, small builders and one person operations are below them and correctly have no VAT number at all. A tradesperson who tells you they are not VAT registered is very probably telling the truth about a perfectly ordinary situation.
What should concern you is the opposite: an invoice that charges you VAT while showing no VAT number, or showing one that VIES rejects. Being charged VAT by someone not registered to collect it is the actual red flag.
What it proves about the business
Nothing beyond tax registration.
A valid VAT number means the business is registered for VAT. It is not evidence of competence, insurance, solvency or good standing. It is not a licence and no one assessed the business before issuing it.
For who you are actually contracting with, use the Companies Registration Office. For whether they are entitled to do the work, use the relevant register, if one exists for that trade.
Checked . Registers move and bodies get renamed. If a link here is dead, the register almost certainly still exists somewhere else on the same organisation's site.