WebMCP Everywhere

A browser extension carrying community-maintained WebMCP adapters — small scripts that register tools into sites that never shipped their own. Install it, point any agent at one local address, and that agent gains real tools on the sites you already have open.

You need Google Chrome 149 or later, and Node.js 20 or later. The WebMCP origin trial runs from Chrome 149 to Chrome 156.

Install it

npx webmcp_everywhere

If you unzipped this folder from a release rather than installing from npm, run the same command out of the folder instead:

node webmcp_everywhere.mjs

Either way it copies this folder to ~/.webmcp_everywhere/installation, and registers the native messaging host so that an agent can reach the browser. It names every path before it writes one. The copy is the point: whatever folder you ran it from may be moved, unzipped again, or emptied by npm, and Chrome keeps an absolute path for both an unpacked extension and a native messaging host.

From then on Chrome starts webmcp_native_host.sh out of the installation folder, as a separate operating system process outside the browser sandbox, with your rights.

One step is left, and only you can take it. Chrome loads an unpacked extension by hand:

1. Open chrome://extensions and turn on Developer mode.
2. Choose Load unpacked, and select ~/.webmcp_everywhere/installation/chrome_extension.

Then point your agent at http://127.0.0.1:8765/mcp, with the bearer token from ~/.webmcp_everywhere/token.

Check it is working

npx webmcp_everywhere status

It asks the running system rather than looking for the extension in Chrome's own files, so it answers about what an agent would really receive: whether a browser is holding the port, whether the extension is connected to it, and which adapters are offering tools in which tabs. It exits 1 when no tools are reaching your agent, and says which step to go and fix. Installing ends with the same answer.

Take it back out

npx webmcp_everywhere uninstall

That removes the registration and the installation folder, and prints what it removed. Your bearer token and any adapters you loaded are left alone. Remove the extension itself at chrome://extensions.

What it does, and what it does not

Read the security model and the permissions before you let an agent act on a site: https://github.com/jeromeetienne/webmcp_everywhere/blob/main/docs/security_model.md