UserScript MCP for claude.ai

A webextension that lets you create user scripts at https://claude.ai, on the free tier too.

Examples

Here are some chats with claude, for show.

• Basic "change background to green" example - https://claude.ai/share/53bf39b3-823a-4de9-a6cb-cb4632bc5032
• Fill reddit username (longer) - https://claude.ai/share/33b465ff-814e-4772-a75f-c943a4551ab0
• Had a mixup with claude (multiple iteration debug) - https://claude.ai/share/b9ddaae5-0f2d-47cd-8947-f2f18a5b4d2a

Installation

Addon Store

• Firefox: https://addons.mozilla.org/en-US/firefox/addon/userscripts-claude-ai/
• Chrome: ...

From Source

$ pnpm i
$ pnpm build:package:all
...Now you load the given .xpi/zip file in your browser...

Usage

1. Preliminary step: log into https://claude.ai, if you aren't already
2. Go to a page where you want to have a user script, e.g. https://example.org
3. Hit the extension button
4. Claude.ai opens in a new tab, and it has access to an MCP
5. Ask Claude to, for example, "make a user script to turn the background green"
6. Claude goes off, it will write the scripts, and instruct you to refresh example.org once done

Development

You can change your target browser in vite.config.js. In my experience, this setup is only slightly buggy & annoying.

$ pnpm dev

I didn't add any svelte components thus far, because the hot reloading was broken.

Credit

Took full advantage of: https://github.com/dnakov/claude-mcp/. Credits there for the MCP hookup processing, which is the most of the work. This code base is a fork of that repo.