What is KSeF?

KSeF (National e-Invoice System)

A system operated by the National Revenue Administration for issuing, transmitting, and storing electronic invoices. From February 1, 2026, it becomes mandatory for the largest companies, and from April 1, 2026, for all taxpayers (according to current Ministry of Finance assumptions).

KSeF API

An application programming interface that connects accounting software with the KSeF system. Thanks to it, software automatically sends and retrieves invoices.

KSeF Taxpayer Application

A free tool from the Ministry of Finance for handling KSeF. You can issue invoices, download them, and manage permissions.

Invoices and Their Elements

Structured Invoice (e-Invoice)

This is not a PDF! It's a set of data in XML format, recorded according to a specific schema. Each piece of information (amount, date, tax ID) has its specific place in the structure.

FA(3) Structure

The invoice schema mandatory in KSeF 2.0 from February 1, 2026. It defines where to place specific data.

KSeF Number

A unique identifier (numbers + letters) assigned to each invoice by the system. It's proof that the invoice was correctly entered.

Entity1, Entity2, Entity3

Entity1 - seller's data
Entity2 - buyer's data
Entity3 - additional data (e.g., company branch, internal unit)

QR Code

A two-dimensional code on invoices issued in OFFLINE mode or transferred outside KSeF. Allows verification of whether the invoice is in the system.

Collective Identifier

A code for a group of invoices. Useful when paying for several invoices with one transfer.

How to Log In?

Trusted Signature (Podpis Zaufany)

A free tool for individuals. Valid for 3 years. The simplest method for logging into KSeF.

National Node (login.gov.pl)

Available from April 1, 2026. You can log in through:

Trusted Signature
mObywatel (mCitizen)
Electronic banking
E-ID card

Qualified Electronic Signature

For individuals. Has the legal force of a handwritten signature. Should contain tax ID or personal identification number.

Qualified Electronic Seal

For companies and partnerships. A digital company stamp with the taxpayer's tax ID.

Token

A string of characters for quick login. Works only until December 31, 2026!

KSeF Certificate

Issued by the Ministry of Finance. There are two types:

Type 1 - for system login
Type 2 - for issuing invoices in OFFLINE mode

Valid for a maximum of 2 years.

System Operating Modes

ONLINE Mode

Normal operating mode. You send an invoice via the internet, the system verifies it and assigns a KSeF number. The buyer has access to it immediately.

Offline24 Mode

When you don't have internet access. You issue the invoice locally and send it to KSeF within 1 business day. You need a KSeF certificate type 2.

Emergency Mode

Only when the Ministry of Finance announces a failure in the Public Information Bulletin. You have 7 business days to send the invoice to the system.

Total Failure

The most serious scenario, announced in the media. You issue invoices outside KSeF and don't send them to the system later.

Permissions in KSeF

Ownership Permissions

Automatically assigned to the company owner. Cannot be revoked. Include:

Issuing invoices
Access to invoices
Managing permissions

Managing Permissions

The ability to grant and revoke access to other people. This is one permission - it cannot be divided.

Permission to Issue Invoices

Allows issuing invoices on behalf of the company (ONLINE and OFFLINE).

Permission to Access Invoices

Access to all company invoices - sales and purchase. This is a separate permission!

ZAW-FA Notification

A form for companies without a qualified seal. You submit it at the tax office to designate a person who will use KSeF on behalf of the company.

Internal Identifier (IDWew)

A code for a branch or unit in the company (format: TaxID-branch code, e.g., 1111111111-33334). Allows limiting access - a branch employee sees only their branch's invoices.

Key Dates

February 1, 2026

Mandatory KSeF for companies with sales exceeding 200 million PLN in 2024
Everyone receives invoices through KSeF

April 1, 2026

Mandatory KSeF for remaining taxpayers

December 31, 2026

End of token usage
End of invoices at cash registers
End of 10,000 PLN monthly allowance

January 1, 2027

Obligation to provide KSeF number for payments between companies
Possibility of penalties for non-compliance

Data according to current Ministry of Finance assumptions.

What to Remember?

An invoice in KSeF is XML, not PDF
KSeF number is proof of invoice issuance
Token works only until the end of 2026
KSeF certificate is the best solution for the future
Invoices are stored in the system for 10 years
In case of problems, call the NRA Helpline or check https://ksef.podatki.gov.pl

KSeF Dictionary - Essential Concepts and Terms You Need to Know