Free KSeF Validator
KSeF (Krajowy System e-Faktur) is Poland's National e-Invoice System, mandatory for all B2B transactions from February 2026. Invoices must be submitted as structured XML in the FA(3) schema format. The system validates, timestamps, and assigns a unique KSeF ID to each invoice.
Checking is free.Finished e-invoice: €1.90 [VAT note].First file every 30 days free.No sign-up.
Your file is used only to check and fix your invoice and to deliver your result. Results are kept so you can download a verified file again for 90 days; validation logs are deleted after 90 days. You can request deletion at any time.
What this check settles
Details are missingYou supply them, we enter them and check again. Amounts, line items and taxes stay unchanged.
The export is structurally brokenYou get the error report for your ERP support: rule, position in the file, expected structure. Free.
The file passes the checkDownload only then, with check protocol, timestamp and checksum. Publicly verifiable.
KSeF profiles
VAT — Standard InvoiceFull VAT invoice with all mandatory fields per FA(3) schema Use: Standard B2B transactions — the most common invoice type in KSeF.
KOR — Corrective InvoiceCorrection of a previously issued invoice Use: Adjustments to amounts, quantities, or VAT rates on existing invoices.
ZAL — Advance Payment InvoiceInvoice for advance or partial payments received Use: Documenting prepayments before goods or services are delivered.
What we check for KSeF
FA(3) XSD schema compliance
NIP (tax number) format and checksum validation
Mandatory header fields (Naglowek) completeness
Seller (Podmiot1) identification and NIP presence
Buyer (Podmiot2) identification and NIP/PESEL format
Invoice date (P_1) not in the future
Invoice number (P_2) uniqueness structure
VAT rate and amount calculation consistency
RodzajFaktury (invoice type) enumeration values
Duplicate detection (NIP + invoice type + number)
Common KSeF rejections
XSD-001XML not conforming to FA(3) schema
440Duplicate invoice detected (NIP + type + number)XSD-NIPInvalid NIP format or checksum failure
XSD-P1Invoice date (P_1) is in the future
XSD-REQMissing mandatory field in Fa section
21405Input data validation error (invalid payload)
All error codes, explained →Where this check runs
Invoice NavigatorPre-submission FA(3) schema check. Validates NIP format, mandatory fields, date rules, and calculation consistency. Catch errors before KSeF rejects your invoice.
Access pointKSeF rejects non-compliant XML immediately — only validated invoices receive a KSeF ID. Error messages reference XSD violations without fix guidance.
ERP built-inSAP, Comarch, and Symfonia generate FA(3) XML but may not validate all schema rules. NIP format errors and missing conditional fields pass through undetected.
KSeF at a glance
System NameKrajowy System e-Faktur
Schema VersionFA(3)
Maintained ByMinistry of Finance (Poland)
B2B MandateFebruary 2026 (large), April 2026 (all)
Key IdentifierNIP (10 digits, mod-11 checksum)
Countries using KSeF
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About KSeF: technical details, history and practice →Peppol BIS validator →UBL 2.1 validator →Related
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