The onChanged event of the cookies API fires when a cookie that the extension can access is set or removed.

Note: When storage partitioning is active, cookies.Cookie.partitionKey contains the description of the cookie's storage partition. When modifying cookies, it's important to pass this value to cookies.set() or cookies.remove() to ensure the extension works with the correct cookie.

Note that updating a cookie's properties is implemented as a two step process:

  1. First, the cookie to be updated is first removed entirely, generating a notification with a cookies.OnChangedCause of overwrite.
  2. Next, a new cookie is written with the updated values, generating a second notification with a cookies.OnChangedCause of explicit.



This API is also available as browser.cookies.onChanged.*.

Events have three functions:


Adds a listener to this event.


Stop listening to this event. The listener argument is the listener to remove.


Check whether listener is registered for this event. Returns true if it is listening, false otherwise.

addListener syntax



A callback function that will be called when this event occurs. The function will be passed the following arguments:


An object containing details of the change that occurred. Its properties are as follows:


A boolean that is set to true if a cookie was removed, and false if not.

A cookies.Cookie object containing information about the cookie that was set or removed.


A cookies.OnChangedCause value representing the underlying reason behind the cookie's change.

Browser compatibility

BCD tables only load in the browser


This example listens for onChanged events and logs details from the changeInfo argument:

browser.cookies.onChanged.addListener((changeInfo) => {
  console.log(`Cookie changed: \n`
    + ` * Cookie: ${JSON.stringify(changeInfo.cookie)}\n`
    + ` * Cause: ${changeInfo.cause}\n`
    + ` * Removed: ${changeInfo.removed}`);

Example extensions

Note: This API is based on Chromium's chrome.cookies API. This documentation is derived from cookies.json in the Chromium code.