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HTML Previewer

Write or paste HTML and see a live rendered preview instantly. Sandboxed, safe, and runs entirely in your browser.

⚡ Live
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HTML Editor
Preview

About HTML Previewer — HTML Previewer Online

The Oneyfy HTML previewer online renders your HTML code in a live sandboxed iframe as you type. Every keystroke updates the preview in real time — no button click, no page reload, no local server required. Paste any HTML snippet, template, or full page and see exactly how it renders in a browser, instantly. The tool supports CSS, JavaScript, and external CDN resources loaded from the internet.

An HTML previewer online is useful in a wide range of situations: developers testing a quick HTML snippet without setting up a local environment, students learning HTML and wanting to see results as they go, designers checking how a component renders before handing off to a developer, and email template builders previewing markup without spinning up an email client. The preview updates with 200ms debounce so even fast typing produces smooth, responsive feedback.

How to Use the HTML Previewer

  1. Type or paste your HTML code into the editor on the left. The preview on the right starts updating immediately as you type. You can paste fragments, full documents, or anything in between.
  2. Click Boilerplate to insert a complete starter HTML5 document including a viewport meta tag and basic body styles. This is the fastest way to start a new HTML experiment from scratch.
  3. Click Wrap in <html> to automatically wrap any bare HTML fragment in a full <!DOCTYPE html><html><head>...</head><body> structure. Useful when you have just the body content and want a complete document for preview.
  4. Use the Width buttons — Full, Tablet (768px), and Mobile (390px) — to preview your layout at different viewport sizes and check how your HTML responds to different screen widths.
  5. Click Copy HTML to copy everything in the editor to your clipboard, or Download to save the current HTML as a .html file to your device.

HTML Previewer Features

The HTML Previewer includes several features that go beyond a basic textarea-to-iframe setup.

  • Live preview with debounce: The preview updates 200 milliseconds after you stop typing, balancing responsiveness with stability. Complex JavaScript in your HTML has time to execute before the next update triggers.
  • Sandboxed iframe: The preview runs in a sandboxed iframe with allow-scripts allow-same-origin permissions. Your HTML can run scripts and load same-origin resources, but the preview is isolated from the tool's own UI so it cannot access the tool page's DOM, cookies, or local storage.
  • Auto-resize: The iframe expands to fit the height of your rendered HTML content, so tall pages do not get cut off or require scrolling inside a fixed-height frame.
  • Responsive width preview: Three preset widths — Full, 768px (tablet), and 390px (mobile) — let you test responsive layouts without browser developer tools or resizing the window.
  • Tab key support: Pressing Tab in the editor inserts two spaces rather than jumping focus away from the textarea, so you can indent your HTML without interrupting your flow.

Tips for Getting the Best Results

These tips help you use the HTML previewer effectively for different types of HTML work.

  • Include CDN links for frameworks and libraries: You can add Bootstrap, Tailwind, Font Awesome, and any other CDN-hosted library by including a <link> or <script> tag referencing the CDN URL. The sandboxed iframe loads external resources over the internet, so a working internet connection is required for CDN dependencies to render correctly.
  • Use Boilerplate as your starting point: Rather than typing a doctype, html, head, and body from scratch, click Boilerplate to get a ready-to-edit template with a viewport meta tag and sensible default styles. Then focus on writing the specific component or content you want to preview.
  • Test mobile layouts at 390px: Click the Mobile width button to constrain the preview to 390px — the approximate viewport width of recent iPhones. This is faster than using browser developer tools for quick checks of whether your layout breaks on mobile.
  • Download to save your work: The editor contents are not persisted between browser sessions — refreshing the page clears the editor. If you write something you want to keep, click Download to save it as an HTML file before leaving the page.
  • Test JavaScript interactivity safely: Any JavaScript you write in the editor runs inside the sandboxed iframe. You can test click handlers, form logic, animations, fetch calls, and localStorage operations without affecting the tool's page or your browser's main session.

Why Use an HTML Previewer Online

A local HTML preview requires opening a file in a browser, switching between your editor and browser, and hitting refresh after every change. An HTML previewer online eliminates that cycle entirely — type once, see the result instantly, iterate faster. There is no setup, no file to save, and no local server to run. The tool works in any modern browser on any operating system, including Chromebooks and devices where installing a code editor is not practical.

Students learning HTML, developers quickly prototyping a component, technical writers checking how an HTML email renders, and anyone who needs to verify a snippet of HTML without spinning up a full project all benefit from a zero-friction live preview tool that runs entirely in the browser.

Frequently Asked Questions about HTML Previewer

Yes. You can include <style> tags for CSS and <script> tags for JavaScript directly in the editor. Inline styles and external stylesheets via CDN also work. Scripts run inside the sandboxed iframe and have access to standard browser APIs including the DOM, fetch, localStorage, and setTimeout. External CDN resources (stylesheets, fonts, JavaScript libraries) load over the internet and work fine with an active internet connection.
The sandboxed iframe isolates the preview from the rest of the tool page. This means your HTML's JavaScript cannot accidentally modify the tool's own buttons or menus, your CSS cannot bleed into the surrounding page, and any errors in your HTML code cannot crash the tool. The sandbox provides a safe, independent rendering context while still allowing scripts and styles to run normally within the preview area.
The editor content lives in your browser's memory for the duration of your session. It is not saved to any server, database, or local storage. When you close the tab or refresh the page, the editor resets to the default boilerplate. To save your work, use the Download button to save your HTML as a local file, or Copy HTML to paste it into your code editor or another tool.
Yes, completely free. There is no sign-up, no account, and no usage limits. You can write, preview, and download HTML at no cost. The tool is available in your browser any time without any installation.
No. The preview is rendered entirely in your browser using an iframe with the srcdoc attribute. Your HTML code is never transmitted to any server. External resources that you reference in your HTML (CDN stylesheets, Google Fonts, API calls made by your JavaScript) do make their own network requests as they normally would, but the HTML source itself stays on your device.
Yes. The HTML previewer works in any modern mobile browser. The two-panel layout stacks vertically on small screens so you can see both the editor and the preview. The editor supports the Tab key for indentation on hardware keyboards. On touchscreen devices, the preview renders your HTML normally within the iframe, and the width buttons still function to test different viewport sizes.
The previewer works with a single HTML document at a time. It can reference external files via CDN URLs (for CSS frameworks, JavaScript libraries, and fonts), but it cannot load local files from your computer or simulate a multi-file project with relative links between pages. For multi-file projects, you will need a local development server. The tool is best suited for single-page HTML snippets and self-contained components.
The preview updates 200 milliseconds after you stop typing. If the preview seems stuck, it may be because your HTML contains a JavaScript error or an infinite loop that is causing the iframe to freeze. Try clearing the editor and pasting a simpler snippet to verify the tool is working. Click Clear to reset the editor and preview to a blank state, then re-enter your content incrementally.