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Ace ( Cloud9 Editor)

Ace is a standalone code editor written in JavaScript. Our goal is to create a browser based editor that matches and extends the features, usability and performance of existing native editors such as TextMate, Vim or Eclipse. It can be easily embedded in any web page or JavaScript application. Ace is developed as the primary editor for Cloud9 IDE and the successor of the Mozilla Skywriter (Bespin) Project.


  • Syntax highlighting
  • Automatic indent and outdent
  • An optional command line
  • Handles huge documents (100,000 lines and more are no problem)
  • Fully customizable key bindings including VI and Emacs modes
  • Themes (TextMate themes can be imported)
  • Search and replace with regular expressions
  • Highlight matching parentheses
  • Toggle between soft tabs and real tabs
  • Displays hidden characters

Take Ace for a spin!

Check out the Ace live demo or get a Cloud9 IDE account to experience Ace while editing one of your own GitHub projects.

If you want, you can use Ace as a textarea replacement thanks to the Ace Bookmarklet.


Previously known as “Bespin” and “Skywriter” it’s now known as Ace ( Cloud9 Editor)! Bespin and Ace started as two independent projects both aiming to build a no compromise code editor component for the web. Bespin started as part of Mozilla Labs and was based on the canvas tag, while Ace is the Editor component of the Cloud9 IDE and is using the DOM for rendering. After the release of Ace at 2010 in Berlin the Skywriter team decided to merge Ace with a simplified version of Skywriter's plugin system and some of Skywriter's extensibility points. All these changes have been merged back to Ace. Both and Mozilla are actively developing and maintaining Ace.

Getting the code

Ace is a community project. We actively encourage and support contributions. The Ace source code is hosted on GitHub. It is released under the Mozilla tri-license (MPL/GPL/LGPL), the same license used by Firefox. This license is friendly to all kinds of projects, whether open source or not. Take charge of your editor and add your favorite language highlighting and keybindings!

git clone git://
git submodule update --init --recursive

Embedding Ace

Ace can be easily embedded into any existing web page. The Ace git repository ships with a pre-packaged version of Ace inside of the build directory. The same packaged files are also available as a separate download. Simply copy the contents of the src subdirectory somewhere into your project and take a look at the included demos of how to use Ace.

The easiest version is simply:

<div id="editor">some text</div>
<script src="src/ace.js" type="text/javascript" charset="utf-8"></script>
window.onload = function() {
    var editor = ace.edit("editor");

To change the theme simply include the Theme's JavaScript file

<script src="src/theme-twilight.js" type="text/javascript" charset="utf-8"></script>

and configure the editor to use the theme:


By default the editor only supports plain text mode; many other languages are available as separate modules. After including the mode's JavaScript file:

<script src="src/mode-javascript.js" type="text/javascript" charset="utf-8"></script>

Then the mode can be used like this:

var JavaScriptMode = require("ace/mode/javascript").Mode;
editor.getSession().setMode(new JavaScriptMode());

Running Ace

After the checkout Ace works out of the box. No build step is required. Open 'editor.html' in any browser except Google Chrome. Google Chrome doesn't allow XMLHTTPRequests from files loaded from disc (i.e. with a file:/// URL). To open Ace in Chrome simply start the bundled mini HTTP server:


The editor can then be opened at http://localhost:9999/editor.html.

Package Ace

To package Ace we use the dryice build tool developed by the Mozilla Skywriter team. To install dryice and all its dependencies simply call:

npm link .

Afterwards Ace can be built by calling


The packaged Ace will be put in the 'build' folder.

Running the Unit Tests

The Ace unit tests run on node.js. Before the first run a couple of node modules have to be installed. The easiest way to do this is by using the node package manager (npm). In the Ace base directory simply call

npm link .

To run the tests call:

node lib/ace/test/all.js


Ace wouldn't be where it is now without contributions. Feel free to fork and improve/enhance Ace in any way your want. If you feel that the editor or the Ace community will benefit from your changes, please open a pull request. To protect the interests of the Ace contributors and users we require contributors to sign a Contributors License Agreement (CLA) before we pull the changes into the main repository. Our CLA is the simplest of agreements, requiring that the contributions you make to an project are only those you're allowed to make. This helps us significantly reduce future legal risk for everyone involved. It is easy, helps everyone, takes ten minutes, and only needs to be completed once. There are two versions of the agreement:

  1. The Individual CLA: use this version if you're working on an in your spare time, or can clearly claim ownership of copyright in what you'll be submitting.
  2. The Corporate CLA: have your corporate lawyer review and submit this if your company is going to be contributing to projects

If you want to contribute to an project please print the CLA and fill it out and sign it. Then either send it by snail mail or fax to us or send it back scanned (or as a photo) by email.


Fax: +31 (0) 206388953

Address: B.V. Keizersgracht 241 1016 EA, Amsterdam the Netherlands

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