As of February 1, 2026, many companies will be required to issue structured invoices and use the National E-Invoice System. Additional entities will be required to do so starting April 1, 2026. Implementing KSeF presents numerous challenges. A way to avoid problems during the KSeF integration process is to use the commercial KSeF REST API. Learn more about this solution and see how it can accelerate and simplify KSeF implementation in your company.
Faster integration
The National E-Invoice System completely changes the paradigm in which businesses document the sale of products and services for VAT purposes. Invoices, which until now were paper or digital in .PDF format, will soon be replaced by structured e-invoices issued within the National E-Invoice System.
For businesses, this translates into significant work and financial investment, requiring them to adapt their existing software (e.g., ERP systems) to meet new legal requirements. However, the integration process can be accelerated by implementing structured invoices and communicating with KSeF using the commercial KSeF REST API and the programming tools provided with it.
The KSeF REST API, available on the kssefapi.pl website, is less complex than the official API developed by the Ministry of Finance – it is more consistent, intuitive, and standardized. This means extending the functionality of company systems to support KSeF requires less work.
What's the main advantage of this solution? Businesses and their IT teams can focus on purely business issues—rather than the technical challenges of implementation. By using a commercial REST API, there's no need to delve into the technical nuances of using the government's KSeF API, such as cryptography, public key infrastructure (PKI), and X.509 certificates.
By using the KSeF REST API, KSeF integration can be quick and efficient – meaning both seamless compliance with legal requirements for e-invoicing and the avoidance of fines. Why is this important? On January 1, 2027, regulations will come into effect, under which businesses violating KSeF obligations will face financial penalties.
You can read more about the benefits of using the KSeF REST API from kssefapi.pl in the article: "Integration with KSeF? Find out why kssefapi.pl is the best solution!"
More useful tools
Integration with the National e-Invoice System involves significant design and programming work and significant technical competency requirements. The commercial KSeF REST API addresses these challenges. Company systems communicate with KSeF via an intuitive, well-documented, and easy-to-use REST API.
By using a commercial API in the implementation process, you can also rely on useful tools that work with it – for example, integration programming libraries. The KSeF REST API from kssefapi.pl offers libraries for the most popular programming languages: PHP, .NET, and Java. More libraries will be released soon.
Thanks to the availability of various libraries, it's easier to integrate software implemented within a company with KSeF—regardless of the programming language it was created in. Examples of how to use the programming libraries are clearly described in the documentation, making it easy to understand how they work.
Other tools that will soon be available from ksefapi.pl include mobile and web applications. These applications will enable employees working off-site to generate structured invoices and submit them to the National e-Invoice System. This is a simple way to expand the functionality of existing systems without the need for significant financial commitments or lengthy implementation processes.
Useful tools—such as integration libraries, a REST API, and applications for interacting with KSeF—significantly reduce integration time. Why? There's no need to reinvent the wheel—when time and reliability are key, it's worth using ready-made, proven solutions.
Better documentation
The documentation for the National e-Invoice System and its API, prepared by the Ministry of Finance, has been criticized by many businesses and integrators for its poor quality. The matter is further complicated by the fact that the KSeF concept has undergone changes over the years, with regulations being amended following consultations, and the system's implementation being postponed several times. As a result, corporate IT departments face a difficult task, the first step of which is understanding how the KSeF works and the technical issues surrounding it.
The KSeF REST API documentation from kssefapi.pl was written to minimize user hassle and ensure successful integration of company systems with KSeF. It provides an accessible and comprehensive description of the KSeF invoice processing process, as well as the API's attributes, classes, and operations. To facilitate understanding of the KSeF REST API, the documentation also includes detailed diagrams illustrating individual operations and the required steps.
Prepared by ksefapi.pl The KSeF REST API documentation is a comprehensive compendium of knowledge that will help the implementation team quickly and easily learn how KSeF works, then integrate their company software with the National e-Invoice System and adapt it to the upcoming new VAT e-invoicing regulations. For companies, this not only saves time and resources but also increases competitiveness – they can be KSeF-ready long before issuing invoices becomes mandatory.
Integration with KSeF? Find out why ksefapi.pl is the best solution!
