MPContribs enables materials researchers to contribute experimental and theoretical materials data to Materials Project (MP). Data on MPContribs is collectively maintained as annotations to existing MP materials and automatically exposed to over 130,000 MP users. MPContribs disseminates contributions as preview cards on MP's materials details pages, in form of domain-specific interactive landing pages on its portal, and programmatically through its API. MPContribs deployments dedicated to datasets for Machine Learning and from DOE Light Sources are currently being built up.