An HTM file is an HTML webpage used by web browsers, such as Google Chrome, Microsoft Edge, and Mozilla Firefox. It may contain hyperlinks and markup language, which defines the elements and layout of a webpage.

HTM file open in Microsoft Visual Studio Code 1 Unless you are a web developer, you will most likely never need to open an HTM file since the HTML in the file is parsed by your web browser. If you want to view the HTML of a webpage, select View Source from the View menu in your web browser (View → Developer → View Source in Chrome). HTM files can also be opened using a basic text editor since the file is saved in a plain text format. However, a source code editor should be used to modify HTM files because they come with helpful coding features. HTM files serve the exact same purpose as .HTML files, but are much less common. The .htm extension arose with the use of Microsoft web development software, such as FrontPage, SharePoint Designer, and Expression Web.