About CTC Engine
Free tools for e-invoices, and plain guides to the formats and the rules behind them.
What CTC Engine is
CTC Engine is a set of free tools for electronic invoices: it converts invoices between CII and UBL, shows an XML invoice as a readable PDF, takes the XML out of a Factur-X or ZUGFeRD PDF and validates an invoice against the official rules. CTC stands for Continuous Transaction Controls: tax systems in which invoice data reaches the tax administration as the transactions happen, as in France with e-invoicing and e-reporting from 2026.
Who it is for
Accountants and bookkeepers who receive XRechnung, Factur-X or ZUGFeRD invoices and need to read or check them; small businesses getting ready for the obligations in France and Germany; developers of invoicing and accounting software who want to test a mapping between CII and UBL.
Standards and versions
The converter reads and writes UN/CEFACT CII D22B and UBL 2.1, in the EN 16931, EXTENDED and EXTENDED-CTC-FR profiles. The validator runs the official rules: EN 16931 (CEN 1.3.16), Factur-X 1.09.2 (the same as ZUGFeRD 2.5.2), EXTENDED-CTC-FR (FNFE-MPE 1.4.0.04), Peppol BIS Billing 3.0.21 and XRechnung 3.0.2 (KoSIT 2.6.0).
How the tools are tested
Before a new version of the converter goes live, official example invoices (from CEN, FNFE-MPE, FeRD and OpenPeppol) and the samples of this site are converted, and every result must pass the schema and the rules of its profile in the validator. The French EXTENDED examples are also compared with their source, value by value. What the converter does not carry yet is said on its pages.
How the guides are written
The guides are written from the official texts: laws, the pages of the tax administrations and the documents of the standards bodies. Each guide that states a rule lists its sources and the date they were last checked, and it is checked against them again whenever it changes. The guides explain; they are not tax or legal advice.
Your invoices
Files are processed on servers in Frankfurt, Germany (EU), only for what you ask, and discarded after about thirty seconds, or ten minutes for a converted invoice. No account, no cookie.
Who publishes it
CTC Engine is published by an individual, on a non-professional basis. The legal notice gives the details.
Report a mistake
Found a mistake in a guide, or a converted invoice that does not look right? Write to the address below with the page or the file concerned.