We propose a method to evaluate the contributions of each participant to the development of a document in a collaborative environment. The algorithm proceeds ex post, by analyzing the different steps that led to the final (assumed satisfying) version of the document. Such an evaluation might be considered as a trust or reputation note, and therefore can be used as an input for trust mechanisms aimed at incentivizing users to contribute efficiently. We implemented this evaluation mechanism in Java, when the document has been developed with Subversion, a version control system used to maintain current and former versions of files.