google-chrome-extension Content scripts Declaring content scripts in the manifest

Example

Content scripts can be declared in manifest.json to be always injected into pages that match a set of URL patterns.

Minimal example

"content_scripts" : [
  {
    "js": ["content.js"],
    "css": ["content.css"]
    "matches": ["http://example.com/*"]
  }
]

This manifest entry instructs Chrome to inject a content script content.js, along with the CSS file content.css, after any navigation to a page matching the match pattern http://example.com/*

Both js and css keys are optional: you can have only one of them or both depending on what you need.

content_scripts key is an array, and you can declare several content script definitions:

"content_scripts" : [
  {
    "js": ["content.js"],
    "matches": ["http://*.example.com/*"]
  },
  {
    "js": ["something_else.js"],
    "matches": ["http://*.example.org/*"]
  }
]

Note that both js and matches are arrays, even if you only have one entry.

More options are available in the official documentation and other Examples.

Important note

Content scripts declared in the manifest will only be injected on new navigations after the extension load. They will not be injected in existing tabs. This also applies to extension reloads while developing, and extension updates after release.

If you need to ensure that currently opened tabs are covered, consider also doing programmatic injection on startup.