FastCompiler
Open HTML Compiler

Free developer tools — no sign-up

Free online code compilers — run code live in your browser

FastCompiler is a free set of in-browser code compilers. Write HTML, CSS and JavaScript and watch it run instantly in a live preview — no download, no account, and nothing ever leaves your device.

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All our tools

Pick a compiler and start coding

Every tool below runs 100% in your browser. No sign-up, no download, no server — just instant live preview with auto-save.

HTML Compiler

Run HTML, CSS and JavaScript together with a live preview, open in a new tab, or download the finished page — all offline.

Run HTML code online

CSS Compiler

Experiment with layouts, colors, flexbox and grid — every CSS change updates the preview live as you type.

Open the CSS playground

JavaScript Compiler

Test JavaScript snippets and see the DOM update live — perfect for debugging logic before it hits your project.

Run JavaScript now

Python Compiler

Run Python 3.12 online without downloading Python — instant console in browser, offline after first load.

Run Python without download

Node.js Compiler

Run Node.js online without installing Node — console.log, async & timers in browser, 100% offline.

Run Node.js without install

HTML to PDF

Convert compiled HTML to PDF — vector, searchable, offline. Also for plain html to pdf.

Convert to PDF now

HTML to Markdown

Paste HTML and get clean Markdown you can use in docs, READMEs and blogs.

Convert to Markdown
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What is an online HTML compiler?

An online HTML compiler is a web app that lets you write HTML, CSS and JavaScript and see the result rendered instantly in a live preview — with nothing to download and no account to create. FastCompiler takes that one step further: every tool runs 100% in your browser, so your code never leaves your device.

Whether you are prototyping a layout, testing a JavaScript snippet, or learning to build for the web, a free online code editor with a live preview is the fastest way to iterate. Open the HTML compiler to write and run HTML, CSS and JavaScript together, use the CSS playground to experiment with styles, test logic in the JavaScript compiler, run Python without download, run Node.js without install, beautify JSON without upload, view CSV without Excel or browse all 9 tools — each one compiles as you type and can export the finished page as a single HTML file.

FastCompiler works offline, auto-saves your work to your browser, and never uploads your code to a server. That makes it ideal for quick experiments, interviews, and any project where you want to keep your code private.

How FastCompiler works

Everything happens in real time inside your own browser. Your code is combined into a single HTML document and rendered instantly in the preview panel — so what you write is what ships.

  1. 1

    Write your code

    Use the built-in editor with tabs for HTML, CSS and JavaScript and VSCode-style syntax highlighting.

  2. 2

    Watch it compile

    Your code auto-compiles and re-renders in the live preview as you type — no refresh needed.

  3. 3

    Ship it anywhere

    Open the result in a new tab, copy the compiled HTML, or download it as a single file to deploy.

Why developers use FastCompiler

⚡

Blazing fast

Lightweight editor with debounced live preview — edits render in under half a second.

🔒

100% offline

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

🧩

VSCode-style editor

CodeMirror-powered tabs for HTML, CSS and JavaScript with syntax highlighting and line numbers.

💾

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 file ready for any host.

Frequently asked questions

Is FastCompiler really free?

Yes. Every compiler on FastCompiler is completely free with no sign-up, no limits, and no paywall. Just open a tool and start coding.

Do I need to download anything to run code online?

No. All FastCompiler tools run entirely in your browser. There is nothing to download or install — open the page and start compiling immediately.

Does my code stay on my device?

Yes. All editing and compilation happens locally in your browser. Your code is never uploaded to any server, which makes FastCompiler a great option for private or prototype work.

Which compilers are available?

FastCompiler offers an HTML code runner (HTML, CSS and JavaScript together), a CSS playground, JavaScript compiler, Python 3.12 compiler without download, Node.js compiler without install, plus JSON formatter, CSV viewer without Excel and more — all offline, no sign-up.

Can I export the code I write?

Yes. Every compiler lets you open the result in a new tab, copy the combined source code, or download it as a single self-contained HTML file ready for any host.

How is FastCompiler different from CodePen or JSFiddle?

Those services are great, but they run in the cloud and require an account. FastCompiler has no sign-up, sends nothing to a server, and auto-saves to local storage — which makes it a natural fit for quick, private and offline work.

Can I use FastCompiler on mobile?

Yes. The compiler layout adapts to smaller screens so you can write and preview code comfortably on phones and tablets.

Where can I learn how to use the compilers?

Start with the documentation, which covers how compilers work and how to write HTML, CSS and JavaScript. For walkthroughs, head over to the blog.