KSeF FA(3) Invoice Lint
Reads a Polish KSeF structured invoice XML and names every line the gateway will reject — with the value the FA(3) schema wants instead. Same engine in the editor and on the free web page: https://getreadystack.com/tools/ksef-fa3-invoice-lint
Why this exists
Since 2026-02-01 KSeF accepts only the FA(3) structure (large taxpayers), and since 2026-04-01 it is the standard for every other active VAT payer. FA(3) lives at a different CRD template than FA(2): http://crd.gov.pl/wzor/2025/06/25/13775/, with kodSystemowy="FA (3)", wersjaSchemy="1-0E" and <WariantFormularza>3</WariantFormularza>.
Most published examples — and most generated code — still carry the FA(2) namespace and the FA(2) attributes. The gateway does validate, but it answers after the call, with a schema code instead of a line number in your file. This extension answers in the editor, on the line.
The transitional period without financial sanctions runs to the end of 2026. From 2027-01-01 a KSeF failure can carry up to 100% of the VAT amount on the invoice, or 18.7% of the gross amount on a VAT-exempt invoice.
What it checks — 18 rules
| Rule |
What KSeF does with it |
fa3_namespace |
Root <Faktura> must carry xmlns="http://crd.gov.pl/wzor/2025/06/25/13775/" |
kod_systemowy |
kodSystemowy="FA (3)" — one space before the bracket |
wersja_schemy |
wersjaSchemy="1-0E" |
wariant_formularza |
<WariantFormularza> must be 3 |
data_wytworzenia |
<DataWytworzeniaFa> is xs:dateTime, not a bare date |
nip_format |
<NIP> is exactly 10 digits — no PL, no dashes |
kod_waluty |
<KodWaluty> is an ISO 4217 three-letter code |
p_1_data |
<P_1> is yyyy-mm-dd, not dd.mm.yyyy |
p_2_numer |
<P_2> invoice number present and non-empty |
rodzaj_faktury |
VAT, KOR, ZAL, ROZ, UPR, KOR_ZAL, KOR_ROZ |
decimal_comma |
Amounts use a dot — a locale comma is unparseable |
amount_space |
No thousands separators inside amount elements |
encoding_utf8 |
Declaration must say encoding="UTF-8" |
adnotacje_flags |
P_16, P_17, P_18, P_18A each present and 1 or 2 |
korekta_ref |
A KOR* invoice must reference <DaneFaKorygowanej> |
placeholder_data |
Sample identifiers such as 1234567890 left in the file |
podmiot_nazwa |
Podmiot1 and Podmiot2 each identified with a name |
penalty_clock |
Counts the errors and the days left before 2027-01-01 |
Measured on the shipped fixtures
_fixtures/clean.xml — a valid FA(3) invoice: 0 findings._fixtures/dirty.xml — the same invoice as an ERP would emit it from FA(2)-shaped code: 23 findings, 22 of them blocking, across 16 of the 18 rules. Six of those lines are the ones almost every generated file gets wrong: the namespace, kodSystemowy, WariantFormularza, the PL 526-231-11-82 NIP, 5166,00 instead of 5166.00, and a date-only DataWytworzeniaFa.- Run on 2026-09-14, the
penalty_clock line reads: 22 blocking errors, 109 days before KSeF penalties resume on 2027-01-01.
Free and full
Free, and complete on its own: one file — the invoice XML open in the editor, or pasted into the web page — with every finding, line numbers and the wanted value. No key, no account.
The full version works on a different axis, scope: KSeF FA(3): Sweep Workspace runs every invoice XML in the folder in one pass and writes a dated REPORT.md — file, line, rule, found value, wanted value — that you keep as your own record for the 2027 penalty regime.
Full version — $29 once, one licence key per person or CI seat, 7-day full refund: https://buy.polar.sh/polar_cl_JEQ1km4V0rbblgu9hwXyGlYM9I06o2ERzguUP2O8bd9
Yardstick: a mid-size KSeF ERP integration in Poland costs PLN 10,000 to PLN 50,000 and takes 2 to 4 months; most of that time is spent making the XML pass validation.
Commands
KSeF FA(3): Check This File — lint the active XML.KSeF FA(3): Sweep Workspace — every invoice XML plus the written report (full version).
Sources
- FA(3) schema, CRD template
2025/06/25/13775, mandatory from 2026-02-01 and 2026-04-01.
- Ministry of Finance: no financial sanctions during 2026; penalties from 2027-01-01, up to 100% of the invoice VAT (18.7% of gross on VAT-exempt invoices).
- Integration cost range: ELTE-S, Ile kosztuje wdrożenie KSeF w 2026 roku.
Not tax advice. Verify against the current Ministry of Finance publication before you file.
