Compose Actions

In a Gmail add-on you can create widgets that have linked actions. One of these kinds of actions is a compose action, which composes a new email draft, optionally filling it using information entered into the add-on UI or information from the open message.

When a compose action is triggered, Gmail executes a callback function to build and return the draft. Gmail then displays that draft in its UI in a standard email compose window, which the user can then edit and send as needed.

Configuring a compose action

To configure a widget to start a compose action when selected, you must do the following:

  1. Make sure your manifest includes the compose action scope: You can use more a permissive scope instead, but should only do so if that scope is absolutely necessary.
  2. Create an Action object and associate it with a callback function you define.
  3. Call the widget's setComposeAction() function, providing it the Action object and specifying the ComposeEmailType.
  4. Implement the callback function that executes the compose action. This function is given an event object as an argument and must do the following:
    1. Create a GmailDraft object.
    2. Build a ComposeActionResponse object using the ComposeActionResponseBuilder class and the GmailDraft object.
    3. Return the built ComposeActionResponse.

You can prefill the GmailDraft you create in the callback function with recipients, a subject, a message body, and attachments. To fill in the draft, data can come from any source, but typically it derives from information provided to the add-on itself, information in the open message, or information gathered from a third-party service. The event object passed to the callback function contains the open message ID and other add-on information you can use to prefill the draft.

You can create the draft as a new standalone message or a reply to an existing message. This is controlled by the ComposeEmailType enum given to the setComposeAction(). You can create reply drafts as single replies or 'reply-all' messages.

Standalone drafts

A standalone draft starts a new thread, which means that it is not a reply to an existing message. You can create a standalone draft with one of the following Gmail service functions:

Reply drafts

A reply draft is part of an existing message thread. Reply drafts are either single replies that only get sent to the sender of a message or "reply all" drafts that get sent to everyone who received that message. You can create a reply draft with one of these Gmail service functions:


The following code snippet shows how to assign a compose action to a button that builds a reply draft.

  var composeAction = CardService.newAction()
  var composeButton = CardService.newTextButton()
      .setText('Compose Reply')
      .setComposeAction(composeAction, CardService.ComposedEmailType.REPLY_AS_DRAFT);

  // ...

   *  Creates a draft email (with an attachment and inline image)
   *  as a reply to an existing message.
   *  @param {Object} e data passed by the compose action.
   *  @return {ComposeActionResponse}
  function createReplyDraft(e) {
    // Activate temporary Gmail add-on scopes, in this case to allow
    // a reply to be drafted.
    var accessToken = e.messageMetadata.accessToken;

    // Creates a draft reply.
    var messageId = e.messageMetadata.messageId;
    var message = GmailApp.getMessageById(messageId);
    var draft = message.createDraftReply('',
            htmlBody: "Kitten! <img src='cid:kitten'/>",
            attachments: [
            inlineImages: {
              "kitten": UrlFetchApp.fetch('')

    // Return a built draft response. This causes Gmail to present a
    // compose window to the user, pre-filled with the content specified
    // above.
    return CardService.newComposeActionResponseBuilder()


Gmail Add-ons
Gmail Add-ons