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.

Check your e-invoice

or

Your file is used only to check and fix your invoice, and kept so you can re-download your result.

Supported Profiles

VAT — Standard Invoice

Full VAT invoice with all mandatory fields per FA(3) schema

Use case: Standard B2B transactions — the most common invoice type in KSeF

KOR — Corrective Invoice

Correction of a previously issued invoice

Use case: Adjustments to amounts, quantities, or VAT rates on existing invoices

ZAL — Advance Payment Invoice

Invoice for advance or partial payments received

Use case: 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)

Countries Using KSeF

🇵🇱Poland

Common KSeF Errors

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)
Browse all error guides

Validator vs Access Point vs ERP Built-in

Invoice Navigator

Pre-submission FA(3) schema check. Validates NIP format, mandatory fields, date rules, and calculation consistency. Catch errors before KSeF rejects your invoice.

Access Point

KSeF rejects non-compliant XML immediately — only validated invoices receive a KSeF ID. Error messages reference XSD violations without fix guidance.

ERP Built-in

SAP, 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 Quick Facts

System Name

Krajowy System e-Faktur

Schema Version

FA(3)

Maintained By

Ministry of Finance (Poland)

B2B Mandate

February 2026 (large), April 2026 (all)

Key Identifier

NIP (10 digits, mod-11 checksum)

KSeF FAQ

What is KSeF?
KSeF (Krajowy System e-Faktur) is Poland's National e-Invoice System. From February 2026, all B2B invoices must be submitted as structured XML through KSeF. The system validates each invoice against the FA(3) schema and assigns a unique KSeF ID.
What is the FA(3) schema?
FA(3) is the latest version of Poland's structured invoice schema, replacing FA(2) from February 2026. It defines over 300 fields — some always mandatory, others conditional on transaction type. The XML must conform to the official XSD published by the Ministry of Finance.
How does KSeF validate NIP numbers?
NIP is a 10-digit Polish tax identification number. KSeF validates the format and mod-11 checksum (weights: 6-5-7-2-3-4-5-6-7). The seller's NIP is mandatory — without it, the invoice cannot be issued. The buyer's NIP determines whether the invoice appears in their KSeF account.
When does the KSeF mandate take effect?
February 1, 2026 for large taxpayers (over PLN 200 million annual turnover). April 1, 2026 for all other VAT-registered entities. January 1, 2027 for micro-entrepreneurs with monthly sales under PLN 10,000.
Is this validator free?
Yes. You can validate up to 10 invoices per month for free. No signup required for basic validation.

Related Formats

Peppol BISUBL 2.1

Learn More About KSeF

Understand the technical details, history, and best practices.

Read the guide

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100% Private Validation

All validation runs entirely in your browser. Your invoice files never leave your device and are never sent to our servers. We can't see your data even if we wanted to.