Free Online HTML Viewer

What Is an Online HTML Viewer?

Quick answer: An online HTML viewer takes the HTML you paste or upload and draws the page it describes inside your browser, so you can view HTML online without saving a file first. It is a free HTML viewer, and no account is needed: paste your code in the box above.

Your browser's rendering engine does the drawing. It reads the tags, builds a Document Object Model (DOM), the tree of elements a page is made of, applies the CSS and runs the JavaScript, whether you paste three lines or a full HTML page.

Paste a snippet or upload a saved .html file, and you get an HTML preview online either way. It will not validate, lint or debug HTML, so a broken tag is drawn however the browser guesses it should look.

How to View HTML Code Online

Pasted code needs step one and a scroll; an uploaded file needs steps two and three.

1. Paste or type your code. Click into the text area labeled Enter or Paste HTML and paste HTML code or type it. The frame titled Result, under the Run / View button, redraws on every keystroke as a live HTML preview. It starts out empty, so a blank frame before you type is normal.
2. Upload an HTML file instead. Click Upload File and choose an .html or .htm file; if the dialog hides .htm, show all files or rename it. The code loads into the box, but nothing is drawn yet. A .txt or .xhtml file gets an Invalid File message.
3. Click Run / View. The page scrolls down to the Result card. This step draws an uploaded file, and it is optional for typed code.
4. Scroll, edit, repeat. The frame is a fixed 400 px tall and scrolls inside itself; change the box and the preview refreshes.

Where the preview lives: The Result card sits below the box, and typing never scrolls to it. At 1366 by 900 and at 390 by 844, the frame was mostly or entirely off screen while we typed. Scroll down or press Run / View after pasting. To get back up, jump to the box.

What the Preview Runs: HTML, CSS and JavaScript

JavaScript execution starts when the preview loads and runs again after every edit. Two rules explain most rows below: the sandbox grants scripts one permission, and linked files load only from full web addresses.

The console.log output does not reach the page. Open developer tools (F12 on most Windows and Linux browsers) and read the browser console, because the viewer has no console of its own. Since alert is ignored, write values into the page, for example with document.body.append(String(value)).

Try It: A Snippet You Can Paste

Paste this HTML snippet into the box above and the frame fills with a card and an orange button labeled Run it. Click it and "Click the button." turns into "The script ran." That is CSS, a click handler and a Document Object Model update in 22 lines. Do not confuse that button with Run / View, under the box.

<!DOCTYPE html>
<html>
<head>
  <style>
    body { font-family: Arial, sans-serif; padding: 24px; }
    .card { max-width: 320px; padding: 16px; border: 1px solid #ccc; border-radius: 8px; }
    button { background: #ff4001; color: #fff; border: 0; padding: 8px 14px; border-radius: 6px; }
  </style>
</head>
<body>
  <div class="card">
    <h2>Hello</h2>
    <p id="msg">Click the button.</p>
    <button id="btn" type="button">Run it</button>
  </div>
  <script>
    document.getElementById('btn').addEventListener('click', function () {
      document.getElementById('msg').textContent = 'The script ran.';
    });
  </script>
</body>
</html>

Change the color value or the button text and the preview redraws on the next keystroke.

Why Images, CSS or Links May Not Load in the Preview

Most of these trace back to one mechanic: the preview is a srcdoc frame, so it has no web address of its own and borrows ours. For CSS not loading, a broken image or JavaScript not running, start here.

• Relative paths. A tag with src="logo.png" or href="style.css" uses a relative path, which the browser measures from this website, not your computer. Expect a not found page for /logo.png and the same for linked stylesheets and scripts. Use an absolute URL, meaning the full https address; an http:// stylesheet or script was blocked as mixed content in our tests.
• The base tag. Put <base href="https://your-site.com/folder/"> first inside the head and relative paths resolve there; in our tests an image on another host loaded that way. Keep only one: the MDN Web Docs reference for the base element says the browser obeys just the first.
• In-page anchors. An anchor link such as <a href="#section"> does not scroll the preview; it loads this whole website inside the frame. Two fixes work: put <base href="about:srcdoc"> in the head and the page scrolls, though relative paths then resolve nowhere, or add onclick="document.getElementById('section').scrollIntoView();return false" to the link, which worked with or without an https base. Pick the click handler if you already use an https base.
• Links and frames. A link to another site, or a meta refresh tag, replaces your preview with that site. Some sites refuse framing: a major search engine page did, citing X-Frame-Options, while a video embed loaded. To get your page back, edit the box or press Run / View.
• Cross-origin requests. The preview's origin is null, so fetch() can read the reply to a cross-origin request only if the API allows any origin; in our test a call to our own site went out but hit a CORS error. Errors land in the console (F12), not on the page.

How the Sandbox Contains Your Code

The preview in this online HTML viewer is a sandboxed iframe built with the iframe sandbox attribute set to allow-scripts, and the text in the box reaches it through the srcdoc attribute. We grant that one flag so your JavaScript can run, and we leave out allow-same-origin. The frame therefore gets a null origin, an identity that matches no real site.

Under the same-origin policy that frame is a stranger. In our tests its scripts could not read this page or use cookies, localStorage, sessionStorage or indexedDB, and every attempt threw a SecurityError.

What the sandbox does not stop is outbound traffic. In the same tests a script loaded third-party files, called an API that allows any origin and sent a beacon to another site. Any tag that loads a file or calls an address can send data out.

The preview is built in your browser from the text in the box, and the page has no step that posts your HTML to our server. That describes how this page is wired, not what your code does once it runs: a relative path is requested from this website, and the page itself loads ad and analytics scripts.

The tab can still freeze: a while(true){} loop locked the whole page in our test, editor box included. Close the tab and reopen the page to start clean.

Rule of thumb: Only paste code you trust. The sandbox limits what a script can reach here, not what it can ask other sites to do.

Limits and Quirks to Know Before You Paste

These numbers come from our own tests on one shared host in October 2026, using desktop Chromium 143 and a 390 px wide layout, not other browsers or real phones. Treat them as examples.

• Every edit reloads the preview. Nothing pauses between keystrokes, so scripts run again and anything you typed inside the preview resets. Seven keystrokes ran our test script once when typed back to back and three to seven times with gaps of 10 ms or more. Never build on a run count.
• Size. The tool sets no size cap. In our tests a pasted 1 MB document drew in one to two seconds, 5 MB in three to ten, 20 MB in about 15 seconds on one run and 21 on another, and a 6.8 MB uploaded file in 8 to 12 seconds after Run / View. Element count beats bytes: 10 MB of tiny paragraphs took roughly 25 to 45 seconds. Browser memory is the real limit.
• Preview size. The frame is a fixed 400 px tall and as wide as its card: 885 px in a 1366 px window, 348 px in a 390 px one. There are no device width buttons, so to test a responsive layout, narrow the window or use device mode in dev tools.
• Doctype. In our tests the viewer drew every doctype variant in standards mode or limited-quirks mode, even with no doctype or an old HTML 4.01 one without its web address. A saved file with either of those falls into quirks mode in Chromium, so start full pages with DOCTYPE html and open the saved file once before you ship.
• Files. Uploads are read with UTF-8 encoding. A file in another character encoding, such as Latin-1, shows replacement characters.

What Happens If You Reload, Go Back or Lose Your Connection

The box is a plain text field with no memory of its own. Before a long session, keep a copy in a text file.

• Reload or close the tab. A reload emptied the box and the preview in our headless Chromium test. We did not test a reopened tab, so copy your code out first.
• The Back button. In our test it brought the text back into the box, but the preview stayed blank until we pressed Run / View.
• Connection drops after the page has loaded. Previewing keeps working, because pasting, uploading and Run / View did not contact this website in our test. Anything your code loads from other sites, such as a CDN stylesheet, fails until you reconnect. A reload shows your browser's error page, and the box is empty afterward.
• The site is briefly unavailable. An open page keeps working. A reload during a restart may land on a browser error or a server error page such as a 503, and the box will be empty. We could only simulate this, so treat the exact page as a guess. Wait a minute, then paste again.

HTML Viewer vs HTML Editor: Which One Do You Need?

An online HTML viewer is for code you already have: you paste it and look. Our HTML Editor is for writing content: a visual editor with a toolbar for headings, bold text, links, tables and images. Its HTML appears in a read-only output box next to a Save to HTML file button. With no editable source code view, it is the wrong place to inspect markup.

This viewer is not an HTML validator or an HTML formatter, and it will not debug anything: an unclosed tag passes without a word. For a rules check, use the W3C Nu HTML Checker.

What People Use an HTML Viewer For

Five jobs fit this tool well, and two come with a caution.

• Snippet checks. Test an HTML snippet or CMS embed code before it goes live; markup copied with view page source tends to carry relative paths.
• AI generated HTML. See what the markup draws, but read its script tags first.
• Learning and teaching HTML. Delete a closing tag and watch what the browser makes of it; that is how people learn HTML, and it suits teaching HTML too.
• Layout checks. Check HTML layout on landing page markup, or prototype a layout with inline styles before the real stylesheet exists.
• Email layouts. You can preview email template layouts, but the viewer does not imitate mail apps, so test in the mail app before you send.

Related Free Tools

Once the preview looks right, the next jobs are file size, structured data and the live page.

• HTML Minifier: shrink the markup before it goes live.
• CSS Minifier: trims the style block once the colors settle.
• JavaScript Minifier: does the same for the script block once the handlers behave.
• Schema Markup Validator: a preview never shows structured data, so check your JSON-LD here.
• Meta Tag Analyzer: paste a live page's address and read its title, description and other tags.
• Website SEO Score Checker: audit the live page after you publish it.

For the slower walkthrough, read the step-by-step guide; the reasoning behind the three minifiers is in how to minify HTML, CSS and JavaScript.