# Multi-Browser MCP Proxies — Arc Browser & Chrome Beta Variants

> Companion to 'Chrome MCP Background Proxy' for running parallel, isolated MCP fleets against Arc Browser and Chrome Beta on top of the same cdp-proxy.mjs. Arc-specific proxy auto-discovers the WebSocket path from /json/version (Arc doesn't write a DevToolsActivePort file in the standard location); Chrome Beta proxy points at Beta's own DevToolsActivePort. Lets you run mcp__chrome__*, mcp__beta__*, and mcp__arc__* side-by-side with independent client state and no cross-talk.

## Install

Merge the JSON below into your `.mcp.json`:

# Multi-Browser MCP Proxies — Arc & Chrome Beta

Companion bundle to **Chrome MCP Background Proxy**. Same `cdp-proxy.mjs`
backbone, repointed at Arc Browser and Chrome Beta so you can run independent,
isolated MCP fleets for each browser without losing focus protection or popup
suppression.

## Why a separate proxy per browser

- **Independent login state** — your work Chrome stays untouched while Arc
  drives experiments, or vice versa.
- **Independent debug ports** — Arc and Chrome Beta both write their own
  `DevToolsActivePort` files; the proxy reads each browser's file via
  `--devtools-port-file`.
- **No cross-talk** — each proxy has its own `clientState`, `sessionOwners`,
  and `pendingRequests` map. A Chrome Beta sub-agent can't accidentally
  hijack Arc tabs.

## Files

| File | Default ports | Reads DevToolsActivePort from |
|------|---------------|-------------------------------|
| `arc-mcp-proxy.sh` | proxy `9501` → Arc `9223` | `~/chrome-profiles/arc-DevToolsActivePort` (auto-built from `/json/version` on each launch) |
| `chrome-beta-mcp-proxy.sh` | proxy `9402` → Chrome Beta `9222` | `~/Library/Application Support/Google Chrome Beta/DevToolsActivePort` |

Both wrap the same `cdp-proxy.mjs` from the parent bundle (`Chrome MCP
Background Proxy`). Drop that file into `~/scripts/` first.

## Arc setup

Arc doesn't write `DevToolsActivePort` to a standard location. Launch it with
an explicit debug port and the proxy script will discover the WebSocket path
on its own:

```bash
open -a "Arc" --args --remote-debugging-port=9223
bash ~/scripts/arc-mcp-proxy.sh   # proxy :9501 → Arc :9223
```

`.mcp.json`:

```json
"arc": {
  "command": "bash",
  "args": ["/Users/<you>/scripts/arc-mcp-proxy.sh", "9501", "9223"]
}
```

## Chrome Beta setup

Chrome Beta writes its own `DevToolsActivePort` file under
`~/Library/Application Support/Google Chrome Beta/`. Once Beta is running with
remote debugging enabled (`chrome://inspect/#remote-debugging` → Allow), the
proxy auto-discovers it.

```json
"beta": {
  "command": "bash",
  "args": ["/Users/<you>/scripts/chrome-beta-mcp-proxy.sh", "9402", "9222"]
}
```

## Running all three side by side

```
Claude Code window A → mcp__chrome__*  → :9401 → Chrome stable :9222
Claude Code window B → mcp__beta__*    → :9402 → Chrome Beta   :9222
Claude Code window C → mcp__arc__*     → :9501 → Arc           :9223
```

Three independent proxies, three independent browsers, three sets of MCP
tool namespaces. They never collide.

## Caveat — don't kill cross-session

Heuristics like "kill 9401/9402 because they're not LISTEN" will tear down a
sibling session's MCP. Always check `lsof -nP -p <pid>` for live stdio before
killing anything. See the `Chrome MCP Operations Runbook` skill for the full
cleanup protocol.


---
Source: https://tokrepo.com/en/workflows/multi-browser-mcp-proxies-arc-browser-chrome-beta-variants-deaee53e
Author: henuwangkai