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JustZix vs Tampermonkey / Greasemonkey — what differs, what wins, when to pick which

15 May 2026 · by JustZix Team

Tampermonkey is synonymous with "userscripts" for 15 years now. When someone says "I'm injecting JS into a page", they're probably thinking Tampermonkey by default. JustZix does everything Tampermonkey does, plus userstyles (like Stylus), plus a UI layer that userscripts don't have. This post shows where we differ.

Feature comparison

Where Tampermonkey wins

• @require + external libs — userscripts can import jQuery, Lodash via URL. JustZix requires inline code or fetching in a JS rule.
• GM_xmlhttpRequest — bypass CORS for cross-domain API calls. JustZix uses native fetch — limited by the page's CORS.
• greasyfork.org marketplace — thousands of public userscripts. JustZix has no central registry (intentionally — TTL share).
• Existing userscript collection — if you have 50 installed userscripts, migration is work. JustZix doesn't import .user.js (but you can copy-paste the body into a JS rule).

Where JustZix wins

• In-tab UI layer — action bars with BUTTON/SLIDER/TOGGLE3 visible on the page. Tampermonkey only has GM_registerMenuCommand in the extension popup (invisible until you click the toolbar icon).
• CSS + JS in one rule — userstyle + userscript together, scope=same. Tampermonkey requires a separate Stylus.
• Live editor in the tab — CSS pane / JS pane to iterate without F5.
• Output Console in the tab — debug without DevTools, dedicated JUSTZIX.log channel.
• Snap dashboard — bars + panes arrange into groups. Tampermonkey has no persistent UI outside the popup.

Migrating 3 typical userscripts to JustZix

Script 1: "Auto-skip cookie banners"

Tampermonkey userscript:

// ==UserScript==
// @name     Cookie skip
// @match    *://*/*
// @run-at   document-end
// ==/UserScript==
(function() {
  const obs = new MutationObserver(() => {
    const accept = [...document.querySelectorAll('button')]
      .find(b => /accept all/i.test(b.textContent));
    if (accept) { accept.click(); obs.disconnect(); }
  });
  obs.observe(document.body, {childList: true, subtree: true});
})();

JustZix migration:

1. New folder "Auto-actions"
2. New rule "Cookie skip", scope: *://*/*
3. JS tab: paste the function body (NO IIFE wrapper, NO userscript header)
4. Run-at: JustZix defaults to "document-end" — matches
5. Save

Script 2: "GitHub: copy SHA"

Tampermonkey userscript adds a "Copy SHA" button next to commit hashes. JustZix:

• Rule scope: https://github.com/*
• JS rule: same code observing commit hash elements
• Plus: instead of creating a DOM button, use a BUTTON action "📋 SHA" in the JustZix action bar — visually consistent with other actions

Script 3: "Reddit hide ads"

Tampermonkey userscript hides .promoted elements. JustZix:

• CSS rule (not JS!) — cleaner, faster: .promoted, [data-promoted="true"] { display: none !important; }
• Bonus: add a TOGGLE3 "Mode" (Default / Hide ads / Hide ads+sponsored) with 3 states' CSS variables

CSS-first patterns are often simpler than a JS observer.

Migration pitfalls

• GM_* APIs are different. Tampermonkey: GM_setValue, GM_getValue, GM_xmlhttpRequest, GM_notification. JustZix: chrome.storage.local/sync, native fetch, JUSTZIX.log as the log channel.
• @require has no equivalent. Userscripts can import jQuery via URL. In JustZix you paste inline (~10KB minified) or fetch + new Function (CSP risk).
• Tampermonkey Cloud Sync is paid. JustZix chrome.storage.sync is free but limited 100KB. Above → chrome.storage.local (no sync). In practice: 50-100 rules.
• greasyfork.org has scripts JustZix doesn't. If you depend on a specific greasyfork userscript — migration is spread out (copy body, adapt GM_* calls). Realistically: 50% of userscripts are <100 lines, ~5 min migration.

What's next

• Migrating from Stylish/Stylus — counterpart for userstyles
• Mini-IDE in a tab — what JustZix adds beyond userscripts
• window.JZ + JUSTZIX — JustZix's equivalent of GM_* API

Install JustZix — Tampermonkey can live in parallel. Test 2 weeks, see which one stays.