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May 2025

Browser MCP transport

MCP between browser tabs and iframes through postMessage, using a website’s existing authentication session.

Built with @ethanniser, @r_marked, and @ben_margolius

Source code Original demo post
Browser MCP demo 1 Browser MCP demo 2

The demos use a fork of 0email with an MCP server added. The chat client opens the app in another tab and calls tools through its existing session.

Original idea by Ethan Niser, built together with @r_marked and @ben_margolius.