That Theme Preview is a free online editor for Home Assistant themes. Write or paste theme YAML and see it applied instantly to the real Home Assistant frontend: dashboard cards, sidebar, header, dialogs, history and energy panels, in both light and dark modes. Includes inline color pickers on every hex value, a searchable reference of 600+ theme variables with their live values, import from GitHub or file, export to YAML, and shareable links that reproduce your exact theme. No signup, no ads. Unofficial tool, not affiliated with Home Assistant or the Open Home Foundation.