A JSON file is a file that stores simple data structures and objects in JavaScript Object Notation (JSON) format, which is a standard data interchange format. It is primarily used for transmitting data between a web application and a server. JSON files are lightweight, text-based, human-readable, and can be edited using a text editor.

The JSON format was originally based on a subset of JavaScript but is considered a language-independent format, being supported by many different programming APIs. JSON is commonly used in Ajax Web application programming. It is becoming increasingly popular as an alternative to XML. While many applications use JSON for data interchange, they may not actually save .json files on the hard drive since the data interchange occurs between Internet-connected computers. However, some applications do enable users to save .json files. One example is Google+, which uses JSON files for saving Profile data. After logging in, you can choose the "Data liberation" page and select "Download your Profile data." Mozilla Firefox saves bookmark backups using JSON files. The files are saved to the Firefox user profile directory within a folder called bookmarkbackups. You can also make manual backups of Firefox bookmarks and import them into a different copy of Firefox. To import, open the bookmark Library, click the import/export button in the top bar, choose Restore → Choose File..., and then select your JSON backup file.