A KSeF structured invoice is an XML invoice in the FA(3) logical structure, issued through Krajowy System e-Faktur, Poland's National e-Invoice System run by the Ministry of Finance. In law it only becomes a structured invoice once KSeF gives it an identifying number. FA(3) has replaced FA(2) for every structured invoice since 1 February 2026. Klarbon opens FA(3) files in beta.
What is in an FA(3) file?
| Property | Value |
|---|---|
| Syntax | national XML, published as a template on ePUAP |
| Owner | Ministerstwo Finansów, Poland's Ministry of Finance |
| Current structure | FA(3), in force since 1 February 2026 |
| Parts | header, parties (Podmiot1 seller, Podmiot2 buyer, Podmiot3 others), invoice data, footer, optional attachment |
| Identifier | the KSeF number assigned on acceptance |
The header holds technical data about the file, the party sections hold the seller, the buyer and any further parties such as a factor, and the invoice section holds the lines and amounts (Ministry of Finance, in Polish). The structure, its documentation and sample files are published on the KSeF portal.
Who has to use KSeF?
| From | Who |
|---|---|
| 1 February 2026 | businesses with 2024 sales above PLN 200 million including VAT |
| 1 April 2026 | other businesses within the mandate's scope |
| until 31 December 2026 | invoices outside KSeF still allowed while their monthly total stays within PLN 10,000 including VAT |
Source: Ministry of Finance, in Polish. In the normal online flow, an invoice counts as issued on the day it is sent to KSeF and as received through the system when KSeF assigns its number. The Ministry describes a separate offline24 rule: if sending is later than the date in P_1, the issue date is the date in P_1. This is general information, not tax advice.
How does FA(3) relate to EN 16931?
FA(3) is a national structure, not a UBL or CII profile of EN 16931. Converting between FA(3) and a European format maps fields from one model to the other, and some may have no counterpart.
What does Klarbon do with KSeF invoices?
| Task | Status |
|---|---|
| Open an FA(3) invoice | beta, in open an e-invoice |
| Use it as the source for a conversion | beta |
| Write FA(3) from another e-invoice | beta: every file is validated against the official FA(3) schema before you can download it |
| Check against the Ministry's business rules | not yet |
Klarbon does not log in to KSeF, send invoices to it or receive a KSeF number. Schema validation does not mean KSeF will accept the file.
Related
Frequently asked questions
What is KSeF?
Krajowy System e-Faktur, Poland's National e-Invoice System, run by the Ministry of Finance. It is used to issue, send, receive and store structured invoices.
What is FA(3)?
The logical structure, an XML schema, of the Polish structured invoice. Since 1 February 2026 it is the only structure used for structured invoices, replacing FA(2).
From when must invoices be issued in KSeF?
According to the Ministry of Finance, from 1 February 2026 for businesses with 2024 sales above PLN 200 million including VAT, and from 1 April 2026 for the others, with a small-value relief until 31 December 2026.
Is there English documentation for KSeF?
The official KSeF portal is mainly in Polish. The FA(3) structure, its documentation and sample files are published there and in the central repository of electronic document templates on ePUAP.
Does an FA(3) file made by Klarbon count as a structured invoice?
No. Under Polish VAT law, a structured invoice is one issued through KSeF with a KSeF number. Klarbon writes FA(3) XML but does not send it to KSeF.
Sources
- Ministry of Finance, structured invoice and the FA logical structure (in Polish) ksef.podatki.gov.pl
- Ministry of Finance, FA(3) logical structure (in Polish) ksef.podatki.gov.pl
- Ministry of Finance, from when invoices must be issued in KSeF (in Polish) ksef.podatki.gov.pl