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Multi logo


Create a custom, lightweight macOS app from a group of websites, complete with:

  • Native notifications, file uploads, and dialogs
  • Ad-blocking, provided by
  • Customization options with JSON, CSS, and JavaScript

Watch me create a Slack clone from scratch in 30 seconds (high res video):

Demo GIF

Table of contents

I've also written a few blog posts that discuss some of the decisions behind Multi:


The easiest method is to use Homebrew:

brew install --cask multi

Alternatively, you can manually download and run the latest .dmg from Releases. If you are on macOS 10.13 High Sierra (the minimum supported version), you'll also need to install the Swift runtime from Apple.

JSON configuration

Multi apps store their configuration in a single JSON file. If your app is named Test, then you'll find that file at /Applications/Multi/ The JSON configuration uses the following top-level fields:

Field Name Type Description
tabs Array (Required) Titles and URLs of tabs for this app
windowed Boolean (Optional, default false) Start the app with each tab in its own window
alwaysNotify Boolean (Optional, default false) Show macOS notifications even if your app is currently focused
openNewWindowsWith String (Optional, macOS 10.15+) Override system default browser for external links — value is a bundle identifier like,, or com.mozilla.firefox
openNewWindowsInBackground Boolean (Optional, default false, macOS 10.15+) Determines if browser app becomes active when opening external links

The tabs field is an array of objects with the following fields:

Field Name Type Description
title String (Required) Whatever you want to call this tab
url String (Required) Starting page for this tab
customJs Array of Strings (Optional) Custom JS URLs (see Custom JS/CSS)
customCss Array of Strings (Optional) Custom CSS URLs (see Custom JS/CSS)
basicAuthUser String (Optional) User name credential for requests that use basic access authentication
basicAuthPassword String (Optional) Password credential for requests that use basic access authentication
userAgent String (Optional) Override the default WebKit user agent header

Here's the bare minimum example used in the Slack demo video above:

{ "tabs": [{ "title": "Slack Lite", "url": "" }] }

Here's a fancier example that uses the optional fields referenced above:

  "tabs": [
      "title": "Dancing",
      "url": "",
      "basicAuthUser": "user",
      "basicAuthPassword": "password",
      "userAgent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/15.6 Safari/605.1.15"
      "title": "Walking",
      "url": "",
      "customJs": [ "" ],
      "customCss": [ "" ]
  "windowed": true,
  "alwaysNotify": true,
  "openNewWindowsWith": "",
  "openNewWindowsInBackground": true

If your configuration file fails to decode for any reason, your Multi app will open to the preferences window, where you can fix any issues.

User-agent tip

Before v2.2.0, Multi included a hard-coded user-agent that made it appear like Safari. This behavior caused subtle issues and confusion when the hard-coded user-agent didn't reflect the system WebKit version. Recent Multi versions remove the hard-coded user-agent, but now sites like Slack and WhatsApp complain that your browser is out of date. (Ideally these sites would use feature detection instead of user-agent sniffing to gracefully degrade behavior; alas, the world does not work ideally.)

If your site doesn't work because it thinks you're using an outdated browser, try setting the userAgent config to match your Safari version.

Using the CLI: create-mac-app

You can create and update Multi apps entirely from the command-line with the included script. In fact, the Multi configuration UI just runs this script under-the-hood! The create-mac-app script takes its options as environment variables. For instance, here's how you'd create a bare-minimum app named Test:

MULTI_APP_NAME='Test' /Applications/

When you open Test, you'll be greeted with the preferences window, where you can finish configuring your app. If you'd like to configure your app entirely from the command-line, you can set any of the following variables:

MULTI_ICON_PATH PNG or ICNS path to icon image
MULTI_JSON_CONFIG See JSON configuration
MULTI_OVERWRITE Set to 1 to replace an existing Multi app with the same name

Custom JS/CSS

Multi lets you customize any site by injecting JavaScript and CSS on every page in your app. Each custom JS/CSS file is specified with a URL, which gives you a few options for how you want to manage your customizations:

  1. Host your file online, and use its URL: ex.
  2. Reference a local file on your computer: ex. file:///Users/kofi/workspace/dotfiles/example.js
  3. Encode your script directly in the JSON using Data URIs: ex. data:,console.log%28%27Hello%2C%20from%20Multi%21%27%29%3B%0A

Custom JS/CSS is one of the most important parts of Multi. It lets the main project stay small and focused, while letting you extend it with new features that fit your use case. If you have a neat JS/CSS snippet, you'd like to share, please open an Issue or Pull Request! Here are a few that have come up before:

Fix links in GMail and Google Calendar

Google seems to be doing some trickery here. Instead of allowing the browser to handle the links, they use JS to open a blank popup window, then dynamically set the URL to Presumably all of this is so that they can track you for a few moments on your way out of their app. Custom JS solution:

(() => {
  const listener = e => e.stopPropagation();
  const query = () => document.querySelectorAll('a[target=_blank]').forEach(a => {
    a.removeEventListener('click', listener);
    a.addEventListener('click', listener, true);
  setInterval(query, 400); // wait time between DOM queries, in milliseconds

Reload Slack when it disconnects

Sometimes Slack's WebSocket disconnects and stops loading new messages. It seems like this is either an issue with WebKit or Custom JS solution:

setInterval(() => {
  if (document.body.innerText.includes('Load new messages.'))
}, 90000);

Find in page

Multi doesn't include any search functionality (Cmd-F). Custom JS solution:

(() => {
  const highlightResults = (text, color) => {
    document.designMode = "on"; //
    var selection = window.getSelection();
    selection.collapse(document.body, 0);
    while (window.find(text)) {
      document.execCommand("HiliteColor", false, color);
    document.designMode = "off";

  let mostRecentSearchText = "";
  const search = text => {
    highlightResults(mostRecentSearchText, "transparent");
    highlightResults(text, "rgb(255 255 1 / 50%)");
    mostRecentSearchText = text;

  const input = document.createElement("input");
  input.placeholder = "Search..."; = "10px 15px"; = "15px"; = "3px"; = "solid 1px lightgray";

  const form = document.createElement("form"); = "none"; = "fixed"; = "15px"; = "15px"; = "2147483647"; //
  form.addEventListener("submit", e => {

  const close = document.createElement("a");
  close.innerText = "⨯";
  close.href = "javascript:void(0)"; = "30px"; = "15px"; = "none";
  close.addEventListener("click", e => {
    search(""); = "none";


  document.addEventListener("keydown", event => {
    if (event.metaKey && event.key === "f") {
      event.preventDefault(); = "block";

Drag-and-drop to open URLs

Sometimes you have a URL outside of Multi (maybe in an email), and you want to open it in Multi. Custom JS solution:

document.addEventListener("dragover", e => e.preventDefault());

Preview link targets

Multi doesn't include any hover-to-preview-link-target functionality. Custom CSS solution:

a:hover::after {
  content: attr(href);
  position: fixed;
  left: 4px;
  bottom: 4px;
  padding: 4px;
  font-size: 12px;
  font-family: -apple-system, BlinkMacSystemFont;
  font-weight: normal;
  color: black;
  background: ghostwhite;
  border: solid 1px black;
  border-radius: 1px;

Keyboard shortcuts

Multi's shortcuts should basically match those of other macOS apps:

⌘X Cut ⌘[ Back
⌘C Copy ⌘] Forward
⌘V Paste ⌘R Reload This Page
⌘↑V Paste and Match Style ⌘+/⌘-/⌘0 Zoom in/out/default
⌘A Select All ^Tab Select Next Tab
⌘^F Toggle Full Screen ^↑Tab Select Previous Tab
⌘M Minimize ⌘1 - ⌘9 Select Tab
⌘H Hide ⌘L Copy current URL
⌘W Close Tab ⌘↑T Toggle Tab Bar
⌘Q Quit ⌘↑\ Toggle Tab Overview


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