The TextBundle file format aims to provide a more seamless user experience when exchanging plain text files, like Markdown or Fountain, between sandboxed applications.

Sandboxing is required for all apps available on the Mac and iOS app store, in order to grant users a high level of data security. Sandboxed apps are only permitted access to files explicitly provided by the user - for example Markdown text files. When working with different Markdown applications, sandboxing can cause inconveniences for the user.

An example: Markdown files may contain references to external images. When sending such a file from a Markdown editor to a previewer, users will have to explicitly permit access to every single image file.

This is where TextBundle comes in. TextBundle brings convenience back - by bundling the Markdown text and all referenced images into a single file. Supporting applications can just exchange TextBundles without asking for additional permissions. Beyond being a simple container, TextBundle includes a standard to transfer additional information - to open up new possibilites for future integration.