European VAT Number Validation API
EU-based businesses are required to obtain valid VAT numbers from VAT-registered entities.
Unfortunately, especially for e-commerce systems, there isn't a simple way to check the validity of a European VAT number. The European Commission provides a web site where you can validate VAT numbers by entering them in an HTML form. This is not practical, of course, for web applications.
Enter, the European VAT Number Validation API that I just hacked together on Google App Engine.
You can hit a URL like http://isvat.appspot.com/GB/802311782/ and get a true or a false back as a simple JSON boolean.
Check out the European VAT Number Validation API.
I hope you find it useful.