The goal of this study is to understand how journalistic culture and practices were adapted and how they evolved during a collaborative factchecking project during the 2017 presidential elections in France. The paper explores how a sample of journalists with different backgrounds adjusted, individually and collectively, to the evolution of a complex system which tracked and exposed disinformation in a politically tense context. The research is based on semi-structured interviews with journalists and editors who participated in CrossCheck, Google representatives who funded the project and members of First Draft. A total of 18 in-depth interviews were conducted in June 2017, a few weeks after the project ended. Our findings show that, while some of the project’s partners already had strong reputations in factchecking and debunking, participants agreed that they should not compete for this type of work, and that it should in fact be considered a public service. All journalists who took part in the project, including those who had previously worked on factchecking and verification, reported learning new skills. Collective editorial decision-making allowed otherwise rival newsrooms to make joint decisions about what to report and what to strategically ignore. The increased cooperation between journalists from different newsrooms and the frequency and diversity of their interactions directed towards a common objective obliged them to confront their routines, professional cultures and respective editorial identities.