Frequently Asked Questions

Contents

1. h2Name
   1. h3Name
2. API reference
   1. Properties
      1. propertyName
   2. Methods
      1. methodName
   3. Events
      1. eventName
   4. Types
      1. id

If you don't find an answer to your question here, try the group or the gallery help.

General

What are Google Chrome Extensions?

Google Chrome Extensions are applications that run inside the Google Chrome browser and provide additional functionality, integration with third party websites or services, and customized browsing experiences.

What technologies are used to write extensions for Google Chrome?

Google Chrome Extensions are written using the same standard web technologies that developers use to create websites. HTML is used as a content markup language, CSS is used for styling, and JavaScript for scripting. Because Google Chrome supports HTML5 and CSS3, developers can use the latest open web technologies such as canvas and CSS animations in their extensions. Extensions also have access to several JavaScript APIs that help perform functions like JSON encoding and interacting with the browser.

Are extensions fetched from the web every time the browser is loaded?

Extensions are downloaded by the Google Chrome browser upon install, and are subsequently run off of the local disk in order to speed up performance. However, if a new version of the extension is pushed online, it will be automatically downloaded in the background to any users who have the extension installed. Extensions may also make requests for remote content at any time, in order to interact with a web service or pull new content from the web.

Development

How can I set up Google Chrome for extension development?

As long as you are using a version of Google Chrome that supports extensions, you already have everything you need to start writing an extension of your own. Select Extensions from the Tools menu (or from the Window menu on Mac) and click Developer Mode. From there, you can load an unpacked directory of files as if it were a packaged extension, reload extensions, and more. For a complete tutorial, please view this getting started guide.

Can I make cross-domain Ajax requests in an extension?

Yes. Extensions can make cross-domain requests. See this page for more information.

Can I use 3rd party web services in my extension?

Yes. Google Chrome Extensions are capable of making cross-domain Ajax requests, so they can call remote APIs directly. APIs which provide data in JSON format are particularly easy to use.

Can I use OAuth in my extensions?

Absolutely, there are extensions which use OAuth to access remote data APIs. Most developers find it convenient to use a JavaScript OAuth library in order to simplify the process of signing OAuth requests.

What UI controls can I create for my extension?

Extensions use HTML and CSS to define their user interfaces, so you can use standard form controls to build your UI, or style the interface with CSS, as you would a web page. Additionally, your extension may add buttons to the Google Chrome browser itself. See browser actions and page actions for more information.

Can I load DLLs in my extension?

Yes, using the NPAPI interface. Because of the possibility for abuse, though, we will review your extension before hosting it in the Google Chrome Extensions Gallery.

Can Google Chrome Extensions encode/decode JSON data?

Yes, because V8 (Google Chrome's JavaScript engine) supports JSON.stringify and JSON.parse natively, you may use these functions in your extensions as described here without including any additional JSON libraries in your code.

Can I store data locally in my extension?

Yes, extensions can use localStorage to store string data permanently. Using Google Chrome's built-in JSON functions, you can store complex data structures in localStorage. For extensions which have the need to execute SQL queries on their stored data, Google Chrome implements client side SQL databases which may be used as well.

How much data can I store in localStorage?

Extensions can store up to 5MB of data in localStorage.

Can I create an options menu for my application?

You can let users set options for your extension by creating an options page which is a simple HTML page that will be loaded when a user clicks the "options" button for your extension. This page can read and write settings to localStorage, or even send options to a web server so that they can be persisted across browsers.

Can two extensions communicate with each other?

Extensions may pass messages to other extensions. See the message passing documentation for more information.

What debugging tools are available to extension developers?

Google Chrome's built-in developer tools can be used to debug extensions as well as web pages. See this tutorial on debugging extensions for more information.

Can extensions use Google Analytics?

Yes, since extensions are built just like websites, they can use Google Analytics to track usage. However, we strongly advise you to modify the tracking code to pull an HTTPS version of the Google Analytics library. See this tutorial for more information on doing this.

How do I determine which version of Google Chrome is deployed to which channel?

To determine which version of Google Chrome is currently available on each of the different platforms, visit omahaproxy.appspot.com. On that site you will see data in a format similar to:

cf,dev,#.#.###.#,#.#.###.#
cf,beta,#.#.###.#,#.#.###.#
cf,stable,#.#.###.#,#.#.###.#
linux,dev,#.#.###.#,#.#.###.#
linux,beta,#.#.###.#,#.#.###.#
linux,stable,#.#.###.#,#.#.###.#
mac,dev,#.#.###.#,#.#.###.#
mac,beta,#.#.###.#,#.#.###.#
mac,stable,#.#.###.#,#.#.###.#
win,canary,#.#.###.#,#.#.###.#
win,dev,#.#.###.#,#.#.###.#
win,beta,#.#.###.#,#.#.###.#
win,stable,#.#.###.#,#.#.###.#

Each line represents a different platform and channel combination. The listed platforms are cf (Google Chrome Frame), linux, mac, and win. The listed channels are canary, dev, beta, and stable. The two four-part numbers at the end of each line represent the range of versions of Google Chrome currently deployed to that platform-channel combination.

Can I add a content script to chrome:// URLs?

No. The extensions APIs have been designed to minimize backwards compatibility issues that can arise when new versions of the browser are pushed. Allowing content scripts on chrome:// URLs would mean that developers would begin to rely on the DOM, CSS, and JavaScript of these pages to stay the same. In the best case, these pages could not be updated as quickly as they are being updated right now. In the worst case, it could mean that an update to one of these pages could cause an extension to break, causing key parts of the browser to stop working for users of that extension.

The reason that replacing the content hosted at these URLs entirely is allowed is because it forces an extension developer to implement all of the functionality they want without depending on the browser's internal implementation to stay the same.

Why do wildcard matches not work for top level domains (TLDs)?

You cannot use wildcard match patterns like http://google.*/* to match TLDs (like http://google.es and http://google.fr) due to the complexity of actually restricting such a match to only the desired domains.

For the example of http://google.*/*, the Google domains would be matched, but so would http://google.someotherdomain.com. Additionally, many sites do not own all of the TLDs for their domain. For an example, assume you want to use http://example.*/* to match http://example.com and http://example.es, but http://example.net is a hostile site. If your extension has a bug, the hostile site could potentially attack your extension in order to get access to your extension's increased privileges.

You should explicitly enumerate the TLDs that you wish to run your extension on.

Features and bugs

I think I've found a bug! How do I make sure it gets fixed?

While developing an extension, you may find behavior that does not match the extensions documentation and may be the result of a bug in Google Chrome. The best thing to do is to make sure an appropriate issue report is filed, and the Chromium team has enough information to reproduce the behavior.

The steps you should follow to ensure this are:

1. Come up with a minimal test extension that demonstrates the issue you wish to report. This extension should have as little code as possible to demonstrate the bug—generally this should be 100 lines of code or less. Many times, developers find that they cannot reproduce their issues this way, which is a good indicator that the bug is in their own code.
2. Search the issue tracker at http://www.crbug.com to see whether someone has reported a similar issue. Most issues related to extensions are filed under Feature=Extensions, so to look for an extension bug related to the chrome.tabs.executeScript function (for example), search for "Feature=Extensions Type=Bug chrome.tabs.executeScript" which will give you this list of results.
3. If you find a bug that describes your issue, click the star icon to be notified when the bug receives an update. Do not respond to the bug to say "me too" or ask "when will this be fixed?"; such updates can cause hundreds of emails to be sent. Add a comment only if you have information (such as a better test case or a suggested fix) that is likely to be helpful.
4. If you found no appropriate bug to star, file a new issue report at http://new.crbug.com. Be as explicit as possible when filling out this form: choose a descriptive title, explain the steps to reproduce the bug, and describe the expected and actual behavior. Attach your test example to the report and add screenshots if appropriate. The easier your report makes it for others to reproduce your issue, the greater chance that your bug will be fixed promptly.
5. Wait for the bug to be updated. Most new bugs are triaged within a week, although it can sometimes take longer for an update. Do not reply to the bug to ask when the issue will be fixed. If your bug has not been modified after two weeks, please post a message to the discussion group with a link back to your bug.
6. If you originally reported your bug on the discussion group and were directed to this FAQ entry, reply to your original thread with a link to the bug you starred or reported. This will make it easier for others experiencing the same issue to find the correct bug.

I have a feature request! How can I report it?

If you identify a feature (especially if it's related to an experimental API) that could be added to improve the extension development experience, make sure an appropriate request is filed in the issue tracker.

The steps you should follow to ensure this are:

1. Search the issue tracker at http://www.crbug.com to see whether someone has requested a similar feature. Most requests related to extensions are filed under Feature=Extensions, so to look for an extension feature request related to keyboard shortcuts (for example), search for "Feature=Extensions Type=Feature shortcuts" which will give you this list of results.
2. If you find a ticket that matches your request, click the star icon to be notified when the bug receives an update. Do not respond to the bug to say "me too" or ask "when will this be implemented?"; such updates can cause hundreds of emails to be sent.
3. If you found no appropriate ticket to star, file a new request at http://new.crbug.com. Be as detailed as possible when filling out this form: choose a descriptive title and explain exactly what feature you would like and how you plan to use it.
4. Wait for the ticket to be updated. Most new requests are triaged within a week, although it can sometimes take longer for an update. Do not reply to the ticket to ask when the feature will be added. If your ticket has not been modified after two weeks, please post a message to the discussion group with a link back to your request.
5. If you originally reported your request on the discussion group and were directed to this FAQ entry, reply to your original thread with a link to the ticket you starred or opened. This will make it easier for others with the same request to find the correct ticket.