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

  • Native notifications, file uploads, and dialogs
  • Customization options with JSON, CSS, and JavaScript
  • CLI for creating and updating apps
  • Options for tabbed or floating windows

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:

If you enjoy using Multi, please consider showing your appreciation with a donation!

Buy Me a Coffee at


The easiest method is to use Homebrew:

brew install --cask multi

Alternatively, you can manually download and run the latest .dmg from Releases.

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 Titles and URLs of tabs for this app (Required)
windowed Boolean Start this app with each tab in its own window
alwaysNotify Boolean Show macOS notifications even if this app is currently focused
alwaysOnTop Boolean Position this app's window on top of all others
terminateWithLastWindow Boolean Determine if this app closes once all tabs/windows are closed
openNewWindowsInBackground Boolean Determines if browser app becomes active when opening external links
openNewWindowsWith String Override system default browser for external linksvalue is a bundle identifier like,, or com.mozilla.firefox

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

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

Here's a bare minimum example to recreate the Slack demo video above:

{ "tabs": [{ "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": [ "file:///Users/kofi/Documents/dotfiles/main/example.js" ],
      "customCss": [ "" ],
      "customCookies": [
          "name": "login_token_tab",
          "value": "eyJoZWxsbyI6ICJ3b3JsZCJ9",
          "domain": "",
          "path": "/"
  "windowed": true,
  "alwaysNotify": true,
  "alwaysOnTop": true,
  "terminateWithLastWindow": true,
  "openNewWindowsInBackground": true,
  "openNewWindowsWith": ""

If your configuration file fails to decode, you can use the settings window to fix the issues. Optional fields will always default to "empty" values (i.e. false, "", []).

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:

window.addEventListener("DOMContentLoaded", () => {
  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

Find in page

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

window.addEventListener("DOMContentLoaded", () => {
  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

Say 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;
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