Formats: Manifest Files

Contents

1. Field summary
   1. h3Name
2. Field details
   1. default_locale
   2. description
   3. homepage_url
   4. icons
   5. incognito
   6. key
   7. minimum_chrome_version
   8. name
   9. permissions
   10. version
3. API reference
   1. Properties
      1. propertyName
   2. Methods
      1. methodName
   3. Events
      1. eventName
   4. Types
      1. id

Every extension has a JSON-formatted manifest file, named manifest.json, that provides important information about the extension.

Field summary

The following code shows the supported manifest fields, with links to the page that discusses each field. The only fields that are required for every extension are name and version.

{
  // Required
  "name": "My Extension",
  "version": "versionString",

  // Recommended
  "description": "A plain text description",
  "icons": { ... },
  "default_locale": "en",

  // Pick one (or none)
  "browser_action": {...},
  "page_action": {...},
  "theme": {...},

  // Add any of these that you need
  "background_page": "aFile.html",
  "chrome_url_overrides": {...},
  "content_scripts": [...],
  "homepage_url": "http://path/to/homepage",
  "incognito": "spanning" or "split",
  "key": "publicKey",
  "minimum_chrome_version": "versionString",
  "options_page": "aFile.html",
  "permissions": [...],
  "plugins": [...],
  "update_url": "http://path/to/updateInfo.xml"
}

Field details

This section covers fields that aren't described in another page. For a complete list of fields, with links to where they're described in detail, see the Field summary.

default_locale

Specifies the subdirectory of _locales that contains the default strings for this extension. This field is required in extensions that have a _locales directory; it must be absent in extensions that have no _locales directory. For details, see Internationalization.

description

A plain text string (no HTML or other formatting; no more than 132 characters) that describes the extension. The description should be suitable for both the browser's extension management UI and the extension gallery. You can specify locale-specific strings for this field; see Internationalization for details.

homepage_url

The URL of the homepage for this extension. The extensions management page (chrome://extensions) will contain a link to this URL. This field is particularly useful if you host the extension on your own site. If you distribute your extension using the gallery, the homepage URL defaults to the extension's own gallery page.

icons

One or more icons that represent the extension. You should provide icons in at least two sizes — 48x48 and 128x128 pixels. The 48x48 icon is used in the extensions management page (chrome://extensions). The 128x128 icon is used when the user installs the extension. You can also specify a 16x16 icon to be used as the favicon for the extension's pages. The 16x16 icon is also displayed in the experimental infobar feature.

Icons should generally be in PNG format, because PNG has the best support for transparency. They can, however, be in any format supported by WebKit, including BMP, GIF, ICO, and JPEG. Here's an example of specifying the icons:

"icons": { "16": "icon16.png",
           "48": "icon48.png",
          "128": "icon128.png" },

Note: Use only the documented icon sizes.

You may notice that Google Chrome sometimes resizes these icons down to smaller sizes. For example, as of this writing, the install dialog shrinks the 128-pixel icon down to 69 pixels.

Nevertheless, you should use only the documented sizes. The details of Google Chrome's UI may change between versions. These changes are made assuming that extension developers are using the documented sizes. If you use other sizes, your icon may look bad in future versions of the browser.

If you submit your extension to the gallery, you'll need to upload additional images, including a 32x32-pixel logo and at least one screenshot of your extension. For more information on gallery requirements, see the gallery help.

incognito

Either "spanning" or "split", to specify how this extension will behave if allowed to run in incognito mode.

The default for extensions is "spanning", which means that the extension will run in a single shared process. Any events or messages from an incognito tab will be sent to the shared process, with an incognito flag indicating where it came from.

The default for installable web apps is "split", which means that all app pages in an incognito window will run in their own incognito process. If the app or extension contains a background page, that will also run in the incognito process. This incognito process runs along side the regular process, but has a separate memory-only cookie store. Each process sees events and messages only from its own context (for example, the incognito process will see only incognito tab updates). The processes are unable to communicate with each other.

As a rule of thumb, if your extension or app needs to load a tab in an incognito browser, use split incognito behavior. If your extension or app needs to be logged into a remote server or persist settings locally, use spanning incognito behavior.

key

This value can be used to control the unique ID of an extension when it is loaded during development.

Note: Most extensions should not need to use this value. Instead, write your code so that the key value doesn't matter by using relative paths and chrome.extension.getURL().

To get a suitable key value, first install your extension from a .crx file (you may need to upload your extension to the gallery, or package it manually). Then, in your user data directory, look in the file Default/Extensions/<extensionId>/<versionString>/manifest.json. You will see the key value filled in there.

minimum_chrome_version

The version of Google Chrome that your extension requires, if any. The format for this string is the same as for the version field.

name

A short, plain text string (no more than 45 characters) that identifies the extension. The name is used in the install dialog, extension management UI, and the extension gallery. You can specify locale-specific strings for this field; see Internationalization for details.

permissions

An array of permissions that the extension might use. Each permission can be either one of a list of known strings (such as "tabs") or a match pattern that gives access to one or more hosts. These permissions are displayed to users before installation. Permissions might also help to limit damage if your extension is attacked.

If an API requires you to declare a permission in the manifest, then its documentation tells you how to do so. For example, the Tabs page shows you how to declare the "tabs" permission.

Here's an example of the permissions part of a manifest file:

"permissions": [
  "tabs",
  "bookmarks",
  "http://www.blogger.com/",
  "http://*.google.com/",
  "unlimitedStorage"
],

The following table lists the permissions an extension can use.

<img src="chrome://favicon/http://www.google.com/">

version

One to four dot-separated integers identifying the version of this extension. A couple of rules apply to the integers: they must be between 0 and 65535, inclusive, and non-zero integers can't start with 0. For example, 99999 and 032 are both invalid.

Here are some examples of valid versions:

• "version": "1"
• "version": "1.0"
• "version": "2.10.2"
• "version": "3.1.2.4567"

The autoupdate system compares versions to determine whether an installed extension needs to be updated. If the published extension has a newer version string than the installed extension, then the extension is automatically updated.

The comparison starts with the leftmost integers. If those integers are equal, the integers to the right are compared, and so on. For example, 1.2.0 is a newer version than 1.1.9.9999.

A missing integer is equal to zero. For example, 1.1.9.9999 is newer than 1.1.

For more information, see Autoupdating.