MCP Session Bridge

What mcp-session-bridge does

The mcp-session-bridge MCP server gives MCP clients a session_* interface for browser automation. It can either control tabs in the user's existing authenticated browser session through the T3rnel Browser extension, or launch and control a separate browser through Chrome DevTools Protocol (CDP).

The interface returns structured browser data, including page context, form values, snapshots, and screenshots. The bridge itself does not send session cookies to a remote browser. It serves MCP over standard input and output using newline-delimited JSON-RPC, so it can be used by clients that support MCP stdio.

How it works

Extension mode uses several local components. The MCP process forwards requests through an owner-only relay socket to a native messaging host launched by Chrome. The native host communicates with the T3rnel Browser extension, which performs actions against live authenticated tabs. The bridge maps its session_* tools to the extension's browser_* tools and includes reconnect and timeout handling.

Standalone mode follows a different path. The mcp-session-bridge MCP server starts its own CDP browser with a persistent profile and drives it directly. The browser can run headfully or headlessly. This mode is isolated from the user's everyday browser and does not need the extension or a license.

Setup and configuration

Install the bridge as an MCP stdio server and use the setup guide for the target client.

For extension mode, install the T3rnel Browser extension in a supported browser: Chrome, Brave, Edge, Opera, Chromium, or Firefox. The extension's available capabilities vary by browser; Opera lacks the side-panel API and Firefox lacks the debugger API. The repository also provides --install and --uninstall support for registering the native host with Chrome, Chromium, Brave, and Edge.

Standalone mode avoids browser-extension setup. It launches its own CDP browser and uses a persistent profile, with no requirement for access to the user's normal browser.

Tools and capabilities

The bridge exposes a broad set of session_* tools, with session_install available for setup. The extension supplies up to 100 browser tools, while the bridge maintains a published tool list at or below that limit for extension builds. Two lower-priority verbs, session_md_diff and session_check_spelling, may be omitted from the advertised list when necessary, although they can still execute when called by name.

Tool availability in extension mode is subject to the extension's Pro gating and approval gate. The package itself does not enforce a separate license, and standalone mode is free according to the repository documentation.

Limitations and notes

The mcp-session-bridge MCP server requires the T3rnel Browser extension for control of an existing signed-in browser. Its browser-specific capabilities are not identical across Chrome-family browsers, Opera, and Firefox. Standalone mode cannot access the user's everyday browser because it launches a separate one.

The server communicates locally through stdio, relay sockets, native messaging, and CDP rather than through a hosted browser service. Clients must support MCP stdio. The repository lists support for many MCP clients, including Claude Code, Cursor, VS Code, Windsurf, Codex, IntelliJ, Cline, Continue.dev, and Roo Code, as well as any other stdio-compatible client.