Skip to content


Repository files navigation

InboxSDK is a JavaScript library for building apps inside of Gmail with browser extensions.

  • No DOM Hacking: exposes a high level, declarative API and handles all the DOM manipulation in a performant way
  • Handles edge cases: multiple inboxes, conversation mode on/off, personal vs workspace, preview pane, fullscreen compose, popouts & themes are all handled
  • Constant updates: new versions released as Gmail updates (often before their changes are fully rolled out)

The InboxSDK is developed by Streak. We use the InboxSDK ourselves to build our own product. We're sharing the InboxSDK so we can collaborate with others on integrating with Gmail and with each other's extensions.


The full docs site and relevant repo.


Check out the Quickstart in the docs, but basic summary:


The most basic example of adding a button to a Gmail compose window:

import * as InboxSDK from '@inboxsdk/core';

InboxSDK.load(2, 'YOUR_APP_ID_HERE').then((sdk) => {
  // the SDK has been loaded, now do something with it!
  sdk.Compose.registerComposeViewHandler((composeView) => {
    // a compose view has come into existence, do something with it!
      title: 'My Nifty Button!',
      iconUrl: '',
      onClick(event) {
        event.composeView.insertTextIntoBodyAtCursor('Hello World!');

See for an example extension using the InboxSDK.


This release of the InboxSDK is distributed under the terms of both the MIT license and the Apache License (Version 2.0). The InboxSDK may be used and redistributed according to the terms of either license. These are permissive licenses that do not require modifications or embedding applications to be open source themselves. See LICENSE-APACHE.txt, LICENSE-MIT.txt, and COPYRIGHT.txt for details.

Contribution Guidelines

Please feel free to open issues or pull requests for bug fixes. For feature requests, please open an issue first so we can decide if and how we may want to support the feature. Many features require ongoing maintenance to support as Gmail changes, and we may not want to commit to supporting every requested feature. If we decide not to implement a feature, we may be able to find a way to implement functionality in the InboxSDK to help applications implement the feature themselves.

Development Cycle Essentials

Run yarn to install the necessary dependencies, and run yarn start to start the automatic builder. Then load examples/hello-world/ as an unpacked extension into Google Chrome.

The Chrome Extensions Reloader extension is supported, and if it is detected then it will be triggered whenever any changes are made to any SDK files, so that you don't have to click reload on the test extension yourself on every change. (You'll still need to refresh Gmail!)

When you are working on the InboxSDK, you should test with one of the example extensions in the examples directory. If you are working on a specific feature, find an example extension that uses that feature, or edit a relevant example to use the feature. If you are adding a new feature to the InboxSDK, make one of the examples use the new feature. The new feature should be easily usable in isolation in an example extension, and must not depend on Streak (including Streak's CSS). Any new features that add elements controlled by the extension ought to be styled (positioned) reasonably by the InboxSDK without requiring the extension to include its own non-trivial CSS.

Technology Choices

We've moved our Flow code over to Typescript. There are still a lot of rougher types from our Flow days. If you see types that could be tightened up, consider doing so if you are working around them.

React is done for some UIs, but there's a complication to using it generally: we often need to integrate with elements from Gmail itself or other instances of the InboxSDK. React only works well for the case where there are a lot of elements created and managed by the InboxSDK itself, we have many places where we have to integrate with outside elements, and most of our additions into the page are pretty simple DOM-wise, so we're pretty picky about where we use React.

Fixing Unreproducible Bugs

Gmail frequently delivers rolling updates to users, so that a small percent of users run different versions of Gmail than most people. These different versions of Gmail may visually appear the same but contain internal differences (HTML structure, ajax request/response formats, etc.) that cause compatibility issues for the InboxSDK.

In general, we should try to add remote error logging that makes it obvious whenever Gmail's HTML structure or ajax formats aren't what we expect. For example, if we have code that calls .querySelector(...) on an element and then requires an element to be returned, we should either import and use 'querySelectorOrFail.ts' (which throws an error with a useful message if no element is found), or we should handle null being returned from .querySelector(...) with code like the following:

const insertionPointEl = el.querySelector('.foo .bar');
if (!insertionPointEl) {
  const err = new Error('Could not find FOO element');
  throw err; // or instead of throwing, do some graceful fallback instead.

If we started seeing that error in our logs, and we weren't able to reproduce the issue locally, then you can log the HTML of the unexpectedly-different element by passing an object as the details parameter to any of Logger's methods. Whenever we log HTML of elements in Gmail, we must either use an HTML censoring function (so we don't risk getting users' message contents; use either censorHTMLstring(el.outerHTML), or censorHTMLtree(el) if information about the element's parents is useful too), or restrict the logging to only happen for Streak users (by checking the extension's appId with the isStreakAppId.ts function). Same rule of thumb applies for logging ajax request/responses too (see censorJSONTree).

Whenever we update our code for a new Gmail version that isn't completely rolled out, we need to make sure our code continues to support previous versions of Gmail. The best way to guarantee this is to create a unit test which runs the code on all known versions of the HTML. (Ideally, the unit test should even work on the censored HTML directly from an error report! Maybe in the future for specific errors, we could automate the process of taking the censored HTML from an error report and creating a new failing test case using it.)

Build Options

By default, yarn start runs the following command:

yarn gulp default -w --reloader

which builds the SDK, watches all of its source files for changes to trigger rebuilds of the bundle automatically (-w), and tells Chrome to reload its extensions after SDK rebuilds (--reload).

Separate SDK and implementation bundles can be built and a local test server which hosts the remote implementation bundle can be started by running:

yarn gulp default server -w --reloader

Building separate SDK and implementation bundles represents how the production builds will work. When using the local test server to host the platform-implementation bundle, you'll need to run Chrome with the --allow-running-insecure-content flag.


All .ts files under __tests__ and all *.test.ts files are tests executed by Jest. All new tests should be Jest tests.

Implementation Notes


When the --remote flag is used, two main javascript files are created: inboxsdk.js and platform-implementation.js. inboxsdk.js implements the InboxSDK object with the load method. It triggers an AJAX request for platform-implementation.js which is evaluated and creates a PlatformImplementation object.



This contains the code for the global InboxSDK object with the load and loadScript methods.


This is the code that the InboxSDK loader fetches from our server.

When it's executed, it defines a global object containing a function that instantiates a PlatformImplementation object. Calls to InboxSDK.load return a promise that resolves to this object. This object is the object given to the extension.

The PlatformImplementation object instantiates a GmailDriver object and uses it to do its DOM manipulations. The GmailDriver object is not directly exposed to the application. This pattern is used often. For example, each Driver object has a getComposeViewDriverStream() method which returns a Kefir stream of objects following the ComposeViewDriver interface. The PlatformImplementation's Compose object takes the ComposeViewDriver object and instantiates a ComposeView object wrapping it, adding some logic common to both Gmail and Inbox, and this ComposeView object is what is exposed to the extension.


This code ultimately ends up inside of platform-implementation.js. Unlike the rest of the code, it's executed within Gmail's environment instead of the extension's environment. This allows it to access global Gmail variables, and to intercept Gmail's AJAX connections (see xhr-proxy-factory). It communicates with the InboxSDK code in the extension environment through DOM events.

InboxSDK code within Gmail's environment has less coverage from our error tracking system, and is more vulnerable to being affected by or affecting Gmail's own Javascript variables, so we try to minimize what functionality lives in the injected script.

The file "src/injected-js/main.ts" is browserified into "dist/injected.js", which is then included by "src/platform-implementation-js/lib/inject-script.ts" and built into "dist/platform-implementation.js".

Element Detection Notes


CSS selectors should not depend on id values as these are uniquely auto-generated at run-time. CSS class names are randomly strings, but they stay the same long term over many sessions and are dependable for using to find elements.

The account switcher widget in Gmail is built a bit differently, and the notes about Inbox should be referred to instead for it.

Inbox Modern Google

(Inbox support is no more, but this knowledge is true of some newer Google web app code and parts of Gmail.)

Like Gmail, Inbox used a lot of randomly generated class names, but the class names appear to be regenerated every few weeks. CSS class names, id values, jstcache properties, and jsl properties are not dependable for using to find elements. The presence of the id and usually the class properties can be used. CSS child and sibling selectors are useful to use.

Gmail Response Processor Utilities

You can use the ./tools/serialize.js and ./tools/deserialize.js executables to (de)serialize Gmail messages from the command line. You need to have babel-cli installed globally (yarn global add babel-cli) for them to work. Each one reads from stdin and writes to stdout.

If you have a file of JSON containing the Gmail response, you can use jq (brew install jq) to read the string out of the JSON and pipe it into deserialize:

jq -j '.input' ./test/data/gmail-response-processor/suggestions.json | ./tools/deserialize.js