1. A system for updating a web application displayed on a client machine, the system comprising: one or more servers comprising one or more processors operable to: maintain, on one or more storage media, a database of application identifiers identifying instances of one or more web applications on one or more client machines; receive, from a first client machine, a communication identifying a first web application and a first application identifier for an instance of the first web application on the first client machine, the instance of the first web application on the first client machine being associated with a first one or more components, each of the first one or more components associated with a component version identifier indicating a version of the component; determine that the first application identifier is not presently included in the database of application identifiers; generate an updated application identifier for the instance of the first web application on the first client machine based on the component version identifier or identifiers of the first one or more components; store the updated application identifier as one of the application identifiers in the database; and transmit a notification to the first client machine, the notification indicating that the instance of the first web application on the first client machine is out-of-date, the notification comprising the updated application identifier.