Introduction

ScriptCat supports three types of scripts:

Type	When it runs
Page scripts	When you open a matching web page; these are what people usually call userscripts
Background scripts	Without any page, for as long as the browser is open; specific to ScriptCat
Scheduled scripts	On a cron schedule; specific to ScriptCat

Ways to develop

• The built-in editor: create a script on ScriptCat's "Installed Scripts" page; it takes effect when you save.
• VSCode: write in a familiar editor and have each save synced to ScriptCat; see Develop Scripts with VSCode.
• An AI coding agent: have Claude Code, Codex or another agent write the script following ScriptCat's rules, install it into ScriptCat and verify it in your browser; see Developing Scripts with AI.

Reference

• API: the GM APIs and metadata ScriptCat supports.
• CatApi: ScriptCat's own extension APIs.
• Background scripts, subscriptions and user config: what only ScriptCat offers.

To learn userscript development step by step, see our Userscript Development Guide. If you find gaps in the documentation, let us know on GitHub, or send a PR to help improve it.