Offline-first is an approach to software development that prioritizes storing data locally and synchronizing with a server when online. To implement this, developers use client-side databases such as PouchDB and Couchbase Sync Gateway. In this example, a web app was built using Bootstrap, jQuery, PouchDB, and Couchbase Sync Gateway to store contacts offline and synchronize them in real-time when the user is online. The app uses Hoodie Store-client for data persistence and offline sync, allowing users to save data locally first and then push changes to the server. With Sync Gateway installed, the app can synchronize its database with a remote server, enabling cross-device synchronization without an internet connection. This approach provides a good way to ensure that data is available when offline and keeps all connected browser clients in-sync.