Lots of efforts are being made to promote open science practices in scholarly publishing. However, information on the openness of scholarly journals is highly fragmented. There are various data sources that provide information on specific aspects of openness, but there is hardly any integration of these data sources. We propose to create a Journal Observatory, an infrastructure that brings together journal information from different data sources and that makes this information openly available through a single interface. The Journal Observatory will help researchers to adopt open science practices and funders and other organizations to check compliance with open science policies.