Open an .html or .htm file and press cmd+shift+v on macOS or ctrl+shift+v elsewhere.
Why Not HTML Preview?
You can't reliably preview pages that expect a real browser origin.
Traditional HTML preview injects HTML into a webview. Modern HTML Preview serves the file from an HTTP origin, so inline scripts, ES modules, relative fetch(), CSS, images, fonts, anchors, forms, unsaved edits, and asset reloads behave much more like a real browser.
Why Not Live Server?
You can't always forward a port.
Live Server needs a server port in remote workspaces. In some setups, like Remote Tunnels, you cannot do that. Modern HTML Preview works from the editor shortcut without managing a server or port.