Various embodiments provide a commenting system for multiple users to provide and share comments to shared content items. For example, users can share a web link to a collection of content items, such as documents, spreadsheets, photos, and any other media, with other users stored in an online content management system. To enable such functionality, the online content management system can expose an application programming interface to enable third-party service providers to develop and attach a comment interface to content items. Accordingly, such a commenting system can provide a comment interface for concurrent display alongside a respective content item in which users can provide comments to shared content items or to use as notes for their personal content items.