develop-userscripts

Userscript work usually breaks at the runtime and metadata boundary, not in the page logic. Choose the runtime first, declare the minimum permissions up front, then debug in the environment where the script actually runs. Use this skill for: Do not use this skill for full browser extension development or general browser automation outside userscript managers. - writing or fixing a Tampermonkey or ScriptCat userscript - debugging injection timing, missing permissions, CSP workarounds, update checks, or GM_* behavior - deciding between a portable foreground script and ScriptCat-only @background or @crontab - adding config UI with ==UserConfig== - packaging a ScriptCat ==UserSubscribe== bundle or preparing a CloudCat-compatible script - Confirm the manager and browser. On Manifest V3 browsers, ScriptCat may require Allow User Scripts or browser developer mode before scripts run. - Decide page script versus background script before writing code. ScriptCat background scripts cannot touch the DOM. - Start with metadata, not implementation: @match , @grant , @connect , @run-at , and any update URLs.