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.First file every 30 days free.No sign-up.

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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

Poland

KSeF FAQ

What is KSeF?
KSeF (Krajowy System e-Faktur) is Poland's national e-invoicing system. Invoices are issued as structured XML in KSeF, which validates each one against the FA(3) schema and assigns a KSeF number.
What is the FA(3) schema?
FA(3) is the current logical structure of the Polish structured invoice. It replaced FA(2) on 1 February 2026. The XML must conform to the XSD published by the Ministry of Finance.
How does KSeF validate NIP numbers?
NIP is Poland's 10-digit tax identification number. The last digit is a mod-11 check digit with weights 6-5-7-2-3-4-5-6-7. The seller's NIP is mandatory; the buyer's NIP determines whether the invoice appears in the buyer's KSeF account.
When does the KSeF mandate take effect?
1 February 2026 for taxpayers whose 2024 sales exceeded PLN 200 million (and receiving in KSeF for everyone). 1 April 2026 for all other VAT taxpayers. 1 January 2027 for taxpayers with monthly invoiced sales of up to PLN 10,000.
Is checking free?
Checking is free. The first verified download every 30 days is free. After that €1.90 per invoice, or €9 a month for all of them. Checking needs no account. You only pay when a file has passed the check and you download it.
Do you fix my invoice automatically?
No. We never change amounts, line items or taxes. Where mandatory details are missing, you supply them, we enter them and check the file again. If the export from your invoicing system is structurally broken, you get the error report for your software support, free of charge.
Where is my file checked, and is it stored?
On our servers, not in your browser. 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.

Read on

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Your dataYour 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.