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Migrating a userscript from Tampermonkey to a JustZix rule

15 May 2026 · by JustZix Team

You have a Tampermonkey userscript you want to move to JustZix. Most of the code pastes over unchanged — but a few things work differently. This guide walks you through it step by step.

What pastes over unchanged

Plain JavaScript working on the DOM — querySelector, addEventListener, fetch, MutationObserver — behaves identically. The core of a typical userscript goes into a rule's JavaScript tab and works.

The metadata header — cut it, move it to the UI

The // ==UserScript== block is not code — it is configuration. In JustZix its equivalent is the interface:

GM_* functions — what is missing and what replaces it

• GM_addStyle — not needed: use the rule's CSS tab instead of injecting styles from JS.
• GM_setValue / GM_getValue — replace with the page's localStorage if the data can live with the page.
• GM_xmlhttpRequest — JustZix has no CORS-bypassing equivalent; a plain fetch works within the page's CSP.
• unsafeWindow — not needed: rule code runs in the page context anyway, you have direct access to window.

What you gain in return

Migration is not just rewriting. In JustZix you get a hierarchy (folder/group/rule), an action bar of on-demand buttons, on-page dev windows and rule sync across devices — things a userscript manager does not have.

Pitfalls

• A userscript loading an external library via @require — move its code into the rule or load the library in the code itself (within the CSP).
• A script relying on a very early start (@run-at document-start) — JustZix rules start a little later; rarely a problem, but be aware.

See also

• JustZix versus Tampermonkey — comparing the tools' philosophies
• URL patterns — the equivalent of @match
• The folder hierarchy — organization userscripts do not have

Install JustZix — and move your userscripts onto something that grows with you.