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Belgium saved 85% of development effort by forking the German COVID-19 app

Belgium forked its COVID-19 app

Published on: 12/11/2020 News Archived

By basing Coronalert on the German Corona Warn App, Belgium achieved reduced costs, development time and gained transparency.

Earlier this week, an article on the OSOR reported on COVID-19 tracing apps and reusable source code. The article shines a light on the potential of Open Source software licenses, as it gives governments the ability to start with an already existing COVID-19 tracing app by making a fork (a separate copy).


The benefits are clear. The development team doesn’t need to start from scratch and in some cases it might be enough to just adapt the code minimally and thus development time and cost can be radically reduced. In fact, according to media reports, the development of the German COVID-19 tracing app cost around € 20 million. The Belgian government managed to release an app as a fork of the German app at a fraction of the cost, reported by different media to be below € 1 million.

Digging deeper into the making of the Belgian Coronalert app, the OSOR spoke to Bart Preneel, Architect of the app, in charge of coordinating the technical work on Coronalert. Preneel pointed to transparency as a critical reason in the decision not only to open source the Belgian app development, but also to rely on an already established and audited Open Source app with Corona Warn App by the German government. 

The highest priority was given to ensuring the absolute minimisation of data collected by any central instance, in order to ensure that the public can trust Coronalert. The app is based on the DP-3T protocol, itself Open Source, which does not share any personal data.


The Belgian government made the decision in the end of June to develop a common COVID-19 tracing app for Belgium, and after selecting the developer in a call for tenders, development of the app was rapid. This, even though only a small team of developers was working on the app. Preneel said that since the German app served as the basis, 85 percent of the code could be reused, meaning the app could be developed in six weeks. The app was adjusted to the Belgian environment,mostly by adapting the way test results are linked in to the app in an anonymous way and looks largely identical to the German template.

The common basis also meant that the Belgian developers could rely on already audited German code and thus less testing was required, meaning the app could be released after just three weeks of testing. Since the German app is based on the Apache 2.0 license, the Belgian team always had full access to the code. This way, the team could decide which changes on the German app they wanted to incorporate and which not.

The Belgian Coronalert app serves as a strong reminder of how Open Source has the potential to make government digital projects more transparent, cheaper to develop and faster to deploy.