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romaklym/assertify

v0.7.0MIT

Use websites you're logged in to. The agent connects to mcp.assertify.co, which relays to the Assertify companion on your own computer: the browser and your encrypted logins never leave it. It can browse, read, click and type on those sites as you, with send, post, buy and delete paused for your approval.

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Assertify plugin

Assertify lets Claude use websites you're logged in to. You sign in once in a real browser window, the session is saved encrypted on your computer, and Claude can then open that site as you: read pages, click, type, fill in forms, download files and take screenshots. Actions that send, post, buy, delete or connect are paused until you approve them.

The plugin contains:

  • An MCP connection to https://mcp.assertify.co/mcp. It relays each tool call to the Assertify companion on your own computer, where the browser and your saved logins are.
  • A skill (use-websites) that teaches Claude the login → browse → close flow and the safety rules.

It works in Claude Code, Cowork, claude.ai and Codex, as long as the companion is running on your computer.

Install

In Claude Code:

/plugin marketplace add romaklym/assertify
/plugin install assertify@assertify

In Codex:

codex plugin marketplace add romaklym/assertify
codex plugin add assertify@assertify

Then, on the computer whose browser you want to use (needs uv):

uvx assertify-mcp setup
uvx assertify-mcp connect

The first time Claude uses Assertify, it opens an mcp.assertify.co page with a code. Run uvx assertify-mcp link CODE on your computer and confirm the app's name. That links this Claude (or Codex) to your computer. There's no account or password.

How it works, and what is sent where

Claude --MCP + OAuth--> mcp.assertify.co --WebSocket--> assertify connect (your computer) --> browser
  • On your computer: assertify connect runs the open-source assertify-mcp package. It opens one outbound connection to mcp.assertify.co (no open ports). Saved logins are cookies and site storage in ~/.assertify-mcp/profiles/, encrypted with a key kept in your system keychain. Screenshots and downloads go to folders under ~/.assertify-mcp/.
  • mcp.assertify.co: it relays tool calls and their results (page outlines, text, screenshots) between Claude and your computer, and stores none of them. It keeps only what sign-in needs: the registered app's name and redirect address, your computer's ID, and hashed tokens. Your logins, cookies and keychain key never leave your computer.
  • Websites: the browser connects only to the sites you or Claude open. A login can be fenced to a list of allowed domains.
  • Passwords: you type them into the site's own sign-in page in a visible window on your computer. Claude never sees them.
  • Safety pauses: clicks that send, post, buy, delete or connect, and pressing Enter in those places, return a pause for your approval instead of acting.
  • Revoking access: uvx assertify-mcp unlink revokes every app linked to your computer. Stopping assertify connect cuts access right away.

Prefer no server at all? Run uvx assertify-mcp as a local MCP server instead; see the main README.

Getting started

After installing, ask Claude something like:

Log me in to GitHub with Assertify, then show my open pull requests.

A browser window opens on your computer for you to sign in. Close it when you're done, and Claude carries on.

Source and license

Source code, issues and full documentation: https://github.com/romaklym/assertify

Privacy policy: https://github.com/romaklym/assertify/blob/main/PRIVACY.md

MIT licensed. See LICENSE.