TiddlyWiki has two approaches to saving the user data (tiddlers) depending on whether you are using the single file version, or are using the node.js server.

TiddlyWiki on node.js saves each tiddler in a separate text file. For details on the file formats supported for tiddlers on node.js, see Tiddler Files.

The single file version of TiddlyWiki saves the tiddlers within the HTML file. See Data Storage in Single File TiddlyWiki