How to Create Google Chrome Extension, Part 1

This tutorial walks you through creating a simple extension. You’ll add an icon to Google Chrome that, when clicked, displays an automatically generated page. The icon and page will look something like this:

You can develop extensions using any release of Google Chrome, on Windows, Mac, or Linux. Extensions you develop on one platform should run without change on every platform Chrome supports.

Create and load an extension

The extension we’ll walk through creating here is a Browser Action, which adds a button to Chrome’s toolbar whose behavior you can control.

1. Create a folder somewhere on your computer to contain your extension’s code.
2. Inside your extension’s folder, create a text file called manifest.json, and fill it with the following code:
   [sourcecode]{
   "name": "My First Extension",
   "version": "1.0",
   "manifest_version": 2,
   "description": "The first extension that I made.",
   "browser_action": {
   "default_icon": "icon.png"
   },
   "permissions": [
   "http://api.flickr.com/"
   ]
   }[/sourcecode]
3. Copy this icon to the same folder:
   Download icon.png
4. Load the extension.
   1. Bring up the extensions management page by clicking the wrench icon  and choosing Tools > Extensions.
   2. If Developer mode has a + by it, click the + to add developer information to the page. The + changes to a -, and more buttons and information appear.
   3. Click the Load unpacked extension button. A file dialog appears.
   4. In the file dialog, navigate to your extension’s folder and click OK.

If your extension is valid, its icon appears next to the address bar, and information about the extension appears in the extensions page, as the following screenshot shows.

Add code to the extension

In this step, you’ll make your extension do something besides just look good.

1. Edit manifest.json to add the following line:
   [sourcecode]…
   "browser_action": {
   "default_icon": "icon.png"<b>,
   "default_popup": "popup.html"</b>
   },
   …[/sourcecode]
   Inside your extension’s folder, create two text files called popup.html and popup.js. Add the following code to these files:

   HTML code (popup.html) and JavaScript code (popup.js) for hello_world

2. Return to the extensions management page, and click the Reload button to load the new version of the extension.
3. Click the extension’s icon. A popup should appear that displays the contents of popup.html.

It should look something like this:

If you don’t see the popup, try the instructions again, following them exactly. Don’t try loading an HTML file that isn’t in the extension’s folder — it won’t work!