We ran our e-invoice checker on the EU's example invoices

einvoice-preflight is a free, MIT-licensed checker for UBL, CII and Factur-X invoices. Its built-in rules had only ever been run on invoices we wrote ourselves. On 2026-10-24 we ran them over the 41 example invoices in the CEN EN 16931 test repository. Those files pass the official Schematron, so a finding on one is either our mistake or a flaw in the example.

Result: 0 of 41 passed. 31 files were readable UBL or CII (the rest are EDIFACT, or over our size limit); 29 of those drew findings.

What was wrong

Almost all of it was ours, and almost all of it was arithmetic:

Unit prices rounded to cents before multiplying. A grid operator bills 0.0088 EUR per kWh; we read it as 0.01.
Line allowances and charges ignored, and the price base quantity (BT-149) too.
VAT summed per line. EN 16931 works it out per rate on the summed taxable amount (BR-CO-17); the two differ by a cent often enough to matter.
A second tax total added. A file that states VAT in both the invoice currency and the accounting currency has two TaxTotal elements; we added them.
CII net read from the wrong field, so any CII invoice with a header allowance failed.
Negative quantities rejected. A returned-goods line is legal.
Zero-rate rows colliding. Standard, zero-rated and exempt lines at 0% are different breakdown rows.

After the fixes the arithmetic rules fire on one file in 31 (a Hungarian invoice that rounds VAT to whole forints). Twelve files still draw INV-012, and those are the example data's fault: a line of quantity 2 at price 800 with a net of 800. The official rules never check that, ours does. The other remaining findings are placeholder VAT numbers and IBANs that fail their checksums.

What we take from it

A checker is only as good as the real files it has seen, and a hand-written fixture shares its author's assumptions. The same exercise on real ERP exports is the next step; the README lists what is still untested. The script is eval/official-examples.mjs; point it at a checkout of the CEN repository to reproduce the numbers.

This is a preflight, not a conformance validator or tax advice.