MDN’s new design is in Beta! A sneak peek:

Sends a single message to event listeners within your add-on or a different add-on.

If sending to your add-on, omit the extensionId argument. The runtime.onMessage event will be fired in each page in your add-on, except for the frame that called runtime.sendMessage.

If sending to a different add-on, include the extensionId argument set to the other add-on's ID. runtime.onMessageExternal will be fired in the other add-on.

Add-ons cannot send messages to content scripts using this method. To send messages to content scripts, use tabs.sendMessage.

This is an asynchronous function that returns a Promise.


var sending = browser.runtime.sendMessage(
  extensionId,             // optional string
  message,                 // any
  options                  // optional object


string. The ID of the add-on to send the message to. Include this to send the message to a different add-on. If the intended recipient has set an ID explicitly using the applications key in manifest.json, then extensionId should have this value. Otherwise it should be have the ID that was generated for the intended recipient.
If extensionId is omitted, the message will be sent to your own add-on.
any. An object that can be serialized to JSON.
boolean. Whether the TLS channel ID will be passed into runtime.onMessageExternal for processes that are listening for the connection event.
boolean. Must be True if the message is intended for a PAC file loaded using the proxy API.

Because this function takes two optional arguments, and the mandatory argument can any JSONable object, this API can be ambiguous. The following rules are used:

  • 1-argument form: if one argument is given, it is the message to send, and the message will be sent internally.
  • 2-argument form: if two arguments are given:
    • if the second argument is a valid options argument (meaning, it is an object which contains only properties supported by the browser), then the first argument is the message to send, and the second argument is the options argument. The message will be sent internally.
    • otherwise, the first argument is the extensionId, and the second argument is the message. The message will be sent to the add-on identified by extensionId.
  • 3-argument form: if three arguments are given, the first is the extensionId, the second argument is the message, and the third is the options. The message will be sent to the add-on identified by extensionId.

Note that before Firefox 55, the rules were different in the 2-argument case. Under the old rules, if the first argument was a string, it was treated as the extensionId, with the message as the second argument. This meant that if you called sendMessage() with arguments like ("my-message", {}), then it would send an empty message to the add-on identified by "my-message". Under the new rules, with these arguments you would send the message "my-message" internally, with an empty options object.

Return value

A Promise. If the sender sent a response, this will be fulfilled with the response as a JSON object. Otherwise it will be fulfilled with no arguments. If an error occurs while connecting to the add-on, the promise will be rejected with an error message.

Browser compatibility

ChromeEdgeFirefoxFirefox for AndroidOpera
Basic support26Yes 1454815
1. `runtime.onMessage` listeners in extension views receive the messages they sent.


Here's a content script that sends a message to the background script when the user clicks the content window. The message payload is {greeting: "Greeting from the content script"}, and the sender also expects to get a response, which is handled in the handleResponse function:

// content-script.js

function handleResponse(message) {
  console.log(`Message from the background script:  ${message.response}`);

function handleError(error) {
  console.log(`Error: ${error}`);

function notifyBackgroundPage(e) {
  var sending = browser.runtime.sendMessage({
    greeting: "Greeting from the content script"
  sending.then(handleResponse, handleError);  

window.addEventListener("click", notifyBackgroundPage);

The corresponding background script looks like this:

// background-script.js

function handleMessage(request, sender, sendResponse) {
  console.log("Message from the content script: " +
  sendResponse({response: "Response from background script"});


Example Add-ons


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

Microsoft Edge compatibility data is supplied by Microsoft Corporation and is included here under the Creative Commons Attribution 3.0 United States License.

Document Tags and Contributors

 Contributors to this page: wbamberg, Rob W, jsnjack, Makyen, chrisdavidmills
 Last updated by: wbamberg,