Abstract: Methods, systems, and apparatus, including computer programs encoded on computer storage media, for creating and managing custom timelines. One of the methods includes receiving, from a user using a user account of a social messaging platform, input to a user interface displaying a message timeline of a social messaging platform, the user input requesting that the platform save a first message from the message timeline and, in response, saving the message to a custom timeline of the user account, wherein saving the message to the custom timeline includes associating with the custom timeline an identifier that identifies the first message; monitoring engagements by one or more other accounts with the first message with respect to one or more notification criteria; and in response to determining that the monitored engagements satisfy a trigger condition, providing a notification to the user account associated with the first message through the custom timeline.