What is KSeF? Poland's national e-invoicing system explained
KSeF is the platform every business invoicing in Poland will issue through. Here's what it is, how it works, the FA_VAT format, the KSeF number and UPO, and the mandatory timeline.
What is KSeF? Poland's national e-invoicing system explained
KSeF (Krajowy System e-Faktur — the National e-Invoice System) is Poland's central platform for structured invoices, run by the Ministry of Finance. Unlike Peppol, which is a decentralised network of Access Points, KSeF is a single government hub: you issue an invoice into KSeF, and your buyer retrieves it from KSeF.
How KSeF works
- You create a structured invoice in the FA_VAT XML format.
- Your software sends it to KSeF (via its API), authenticated.
- KSeF validates it, assigns a unique KSeF number, and returns an official
confirmation — the UPO (Urzędowe Poświadczenie Odbioru).
- The invoice is considered issued at the moment KSeF accepts it.
- Your buyer accesses it directly in KSeF.
There's no "send to the customer" step in the Peppol sense — KSeF is the delivery channel for domestic invoices.
The FA_VAT format
Invoices must follow the Ministry's structured schema (FA(2), with FA(3) introduced as the system evolves). It's a defined XML — not a PDF. A PDF can exist as a human-readable visualisation, but the legal invoice is the structured file in KSeF.
The KSeF number and UPO
- KSeF number — the unique ID KSeF assigns; it identifies the invoice
officially.
- UPO — your proof the invoice was received and accepted. Keep it; it's the
equivalent of a delivery receipt.
Who must use it, and when
KSeF becomes mandatory on a phased calendar (after an earlier postponement): larger taxpayers first, then the rest of businesses. Exact dates have shifted before, so confirm your phase with a Polish tax advisor — but the direction is fixed: structured invoicing through KSeF for domestic trade.
Authentication
You identify to KSeF with a qualified electronic signature or seal, a trusted profile, or a token generated inside KSeF for your software. See KSeF integration.
KSeF vs Peppol
- KSeF — Poland's domestic national system; centralised; FA_VAT.
- Peppol — the EU cross-border network; decentralised; UBL/EN 16931.
A Polish business that also trades across the EU deals with both worlds.
Where Eurobillr fits
Eurobillr focuses on Peppol and EU e-invoicing — Belgium, France (via an accredited platform), Italy SDI, Germany XRechnung — so if you invoice across borders from or into Poland, Eurobillr covers the EU/Peppol side. KSeF itself is Poland's domestic system; for domestic Polish issuance you use a KSeF-connected solution. If KSeF matters to your setup, tell us — it helps us prioritise.
Next in this series: KSeF integration · how to issue a KSeF invoice.