SmartKSeF
An integration platform — a KSeF hub — sitting between companies’ ERP systems and Poland’s National e-Invoicing System, the government gateway that became mandatory for large entities on 1 February 2026 and for SMEs on 1 April 2026. Over 300 client organisations use it, among them Empik, Auchan, LuxMed and Crédit Agricole, and it was built for a projected capacity above 20 million e-invoices per year. I worked on the backend from the project’s inception, and led the team building it from 2024.
The law was still being written. The KSeF mandate was amended and its deadline postponed repeatedly across the build, and the Ministry of Finance’s XML schemas moved with it. The team was implementing a specification that would not hold still, so the system had to be structured to absorb regulatory revision as routine maintenance rather than as a rewrite. That is the single most transferable thing about the project.
The product is essentially a shock absorber for an unreliable dependency. Almost everything valuable it does exists because the government gateway cannot be relied upon. XML is pre-validated before submission, so structural errors surface early rather than as a rejection. Invoices are queued when KSeF or the network is unavailable and transmission is retried automatically, so a ministry outage never loses a client’s document. Delivery receipts (UPO) are pulled back and processing statuses pushed to the source systems, and gateway availability is monitored continuously, with alerting on anomalies. The engineering goal was to make an unstable external system invisible to the client.
One platform, many organisations, all of them different. Validation rules for sales and purchase invoices are defined per client. Documents are classified automatically and routed into the right domain system by user-defined rules. Multiple legal entities are managed in one place with per-user access levels, Active Directory integration fits each client’s existing security policy, and notifications reach invoice recipients — including foreign counterparties who have no KSeF access at all. The full processing history is archived for audit and inspection.
I joined at project inception as a junior developer, was promoted twice in three years, and led the five-engineer team from 2024. Backend throughout.
