FastCompiler
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The web's fastest HTML code runner

HTML code runner online — run HTML, CSS & JavaScript free

Run HTML online without downloading anything — type code on the left and watch it run on the right instantly. FastCompiler is a free in-browser HTML code runner with live preview, no sign-up and no server — your code never leaves your device.

Start Running Code Documentation

Features

⚡

Instant live preview

Your HTML, CSS and JavaScript re-render in under half a second as you type — no refresh, no compile button needed.

🔒

100% offline & private

Compilation happens entirely in your browser. Nothing is uploaded, so your code stays on your device.

🧩

Three tabs, one page

Separate tabs for HTML, CSS and JavaScript are merged into a single document in the preview.

💾

Auto-save

Your work is saved to local storage automatically, so it is there when you come back.

↗

Open in new tab

See the compiled result as a real standalone page in a fresh browser tab.

📦

Download & share

Copy the combined HTML or download it as a single self-contained file ready for any host.

How to run HTML code online

Running HTML code online with FastCompiler takes three steps — and the first one is already done, because the editor is right above.

  1. 1

    Write or paste your code

    Type into the HTML tab, or paste a whole page — CSS and JavaScript get their own tabs above the editor.

  2. 2

    Watch it run live

    The preview renders automatically as you type, so you can test changes instantly without installing anything.

  3. 3

    Export or share

    Open the result in a new tab, copy the combined source, or download it as a single HTML file.

Popular use cases

Learning HTML & CSS

Get instant feedback on every tag and rule. Iterate on a small demo until the concept clicks — no install, no setup.

Read the HTML guide

CSS prototyping

Sketch a layout, hover state, or animation and see it render in real time before you touch your real codebase.

Open the CSS playground

JavaScript experiments

Test an event handler, a fetch call, or a DOM trick in a sandbox where nothing can crash your main project.

Run JavaScript online

Building small widgets

Create a button, a pricing card, or a whole micro-site, then download it as a self-contained file to drop anywhere.

Export & publish

Email & HTML templates

Assemble an HTML email or template, verify it in the live preview, and copy the combined source into your CMS.

Open in new tab

AI-assisted coding

Ask an assistant to draft a tiny page, paste it in, compile it, and iterate — the tightest loop for turning prompts into working pages.

Coding with AI

Copy-paste examples

3 HTML examples to try right now

Paste into the editor above and watch the preview update live. By Juwel, last updated September 8, 2026.

1. Semantic article card (SEO-friendly)

<main>
  <article>
    <h1>My first compiled page</h1>
    <p>Built with FastCompiler — no build step.</p>
    <a href="/blog">Read the guides</a>
  </article>
</main>

2. Accessible form (labels + inputs)

<form>
  <label for="email">Email</label>
  <input id="email" type="email" required placeholder="[email protected]" />
  <button type="submit">Subscribe</button>
</form>

3. Details accordion without JavaScript

<details>
  <summary>Why offline?</summary>
  <p>Your code never leaves your device.</p>
</details>

Learn why this matters: SEO-friendly HTML tags, details accordions, heading outline test.

Limitations & how it compares

FastCompiler merges your three tabs into one document (<style> in <head>, <script> before </body>) and renders with your real browser — no emulation drift. It is ideal for prototypes, emails and learning. It is not a backend: no npm, no database, no server includes. For Python use the Python compiler, for Node-like logic the Node.js compiler.

vs CodePen/JSFiddle: cloud + accounts vs FastCompiler's offline localStorage auto-save and one-file download for any static host. Reviewed by Juwel, founder & editor.

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CSS Compiler

Experiment with layouts, colors, flexbox and grid — every change updates live in the preview panel.

Open the CSS playground

JavaScript Compiler

Run JavaScript snippets and see the DOM update live without reloading a single tab.

Run JavaScript now

HTML Tags Reference

Every HTML tag explained with live examples you can copy straight into the code runner.

Browse the reference

Frequently asked questions

How can I run HTML code online without downloading anything?

Open the FastCompiler HTML code runner above, paste or type your HTML, CSS and JavaScript into the editor tabs, and the preview updates live. Everything runs in your browser — nothing to download or install.

Is there a free online HTML compiler?

Yes. FastCompiler is a free online HTML compiler with no sign-up, no limits and no paywall. You also get CSS and JavaScript tabs, live preview, and one-click download.

Can I run HTML and CSS together online?

Yes. Use the HTML tab for markup and the CSS tab for styling — the compiler merges them into one document and renders the combined result in the live preview.

Does the HTML code runner work on mobile?

Yes. The editor and preview stack vertically on small screens, so you can write and run HTML code comfortably on phones and tablets.

Can I download the HTML file I write?

Yes. Click Download to save a single, self-contained HTML file, or click Open in new tab to see the compiled page on its own.

Does FastCompiler upload my code to a server?

No. Compilation happens entirely in your browser and nothing is uploaded. Your code is auto-saved to your device's local storage only.