What is HTML Viewer?
HTML Viewer is a live interactive sandbox tool that renders HTML code into a real-time browser preview pane. Testing HTML code snippets or previewing HTML email templates usually requires saving local files and opening them in a browser. With HTML Viewer, you can type or paste HTML, CSS, and inline JavaScript into the editor and view the rendered result live in a sandboxed iframe immediately.
How to use HTML Viewer
Paste or type your HTML markup into the code editor panel on the left. The right pane automatically updates with a live visual render of the output. Toggle between desktop and mobile viewport container widths to inspect responsive behavior. You can also view the rendered DOM output in full-screen mode.
Key features
- Real-time live HTML, CSS, and JS preview updating as you type
- Sandboxed isolated iframe execution environment
- Toggleable desktop and mobile responsive device viewports
- Supports external CDN stylesheets (Tailwind, Bootstrap, Google Fonts) and scripts
- Full-screen preview toggle
- Instant copy and code download commands
- 100% private client-side operation
Common use cases
- Previewing HTML email templates for cross-client visual validation
- Prototyping component layouts and landing page sections quickly
- Testing custom CSS button styles, cards, and typography
- Inspecting dynamic HTML output snippets from backend APIs
- Testing responsive layout behavior across device widths
Technical details & standards
The preview engine renders content inside a sandboxed <iframe> HTML element with appropriate security attributes, ensuring isolation from the main app environment while still allowing CSS rendering and external CDN script/style resource loading. All rendering happens client-side inside your browser, making it completely private and fast.
Frequently asked questions
Can HTML Viewer load external CSS frameworks like Tailwind or Bootstrap?
Yes! Add standard <link> tags referencing external CDNs (e.g. cdnjs or unpkg) and they will render live in the preview.
Is the preview environment secure?
Yes. The preview uses a sandboxed iframe to isolate execution safely within your browser.
Is my data safe?
All processing happens entirely in your browser. Your data never leaves your device and is never sent to or stored on a server.
Does it work offline?
Yes. Once the page has loaded, most tools keep working without an internet connection.