open-claude-in-chrome

The official Claude in Chrome extension gives Claude Code full browser automation — as long as you stay within Anthropic's allowlist of "safe" sites. Open Claude in Chrome is a clean-room reimplementation that strips the restrictions while keeping all 21 MCP tools and matching the official extension's performance.

What's Different

Blocked Domains in the Official Extension

Open Claude in Chrome has none of these restrictions.

Does it actually match the official extension?

Yes — and rather than assert it, here is a benchmark. Read the full study →

17 arms, each run over the same 12 held-out tasks from the REAL web-agent benchmark, same model and effort throughout (Sonnet, medium). What it found:

• Parity, out of the box. The official extension and this harness, both cold, are statistically indistinguishable: 2.04 vs 1.95 min/task and 31.4 vs 32.6 turns, at p=0.44 and p=0.67 on a paired permutation test, with identical accuracy. They differ only in per-action overhead — 0.31s vs 0.12s per browser action, 2.7× less.
• A higher ceiling. The best method in the study lands 23% fewer turns and 15% less time than the official extension, at 11/12 tasks passed against 8/12. Distil prior runs into a short per-site recipe, put it in the task prompt, and start from a warmed-up session.
• What actually helps. Mounting raw prior experience on disk costs more than it returns (the agent spends 3.5× longer before its first browser action); compressing it into the prompt is what pays. Context is the dominant latency term at +1.9s per turn per 100k tokens, so more context is not free.
• Recordings. This harness records raw, four-track browser traces and defers the analysis; Claude Cowork analyses each recording at capture time and keeps only the result. Distilled the same way by the same model, the raw recordings win both regimes — 6.6 fewer turns and 6.4 fewer minutes when the material has to fit in a prompt (p=0.012, p=0.008).

Caveats are in the writeup, not hidden: the task set saturates, one task's grading is ambiguous, and repeat runs of an identical configuration vary by 10–20%, so treat single-digit differences as noise.

Architecture

Default:

Claude Code <--stdio MCP--> mcp-server.js <--TCP--> native-host.js <--native messaging--> Extension <--> Browser

Code mode / hybrid (additive — mcp-server.js is reused unchanged as the upstream):

Claude Code <--stdio MCP--> server-{codemode,hybrid}.js
                              |  spawns + proxies via MCP
                              v
                            mcp-server.js (child) <--TCP--> native-host.js <--native messaging--> Extension <--> Browser
                              ^
                              |  HTTP tool-callback
                              |
                            workerd (wrangler dev sidecar)
                              |  Worker Loader → V8 isolate
                              v
                            sandboxed Worker runs LLM-written code

Three components:

1. Extension — Manifest V3 with CDP-based browser automation (all 21 tools)
2. MCP Server — Node.js process started by Claude Code, exposes tools via MCP
3. Native Messaging Host — Bridge between the MCP server and the extension

The codemode and hybrid servers add a fourth piece — a wrangler dev subprocess hosting a Cloudflare Worker that runs the LLM-generated code in a V8 isolate. The Worker calls back to the proxy over HTTP for actual tool execution, which is forwarded to the unchanged upstream mcp-server.js.

Installation

One flow, top to bottom, turns everything on — all 21 browser tools, execute_code, and the imitation-learning recorder.

Prerequisites

• Node.js v18+
• Any Chromium browser (Chrome, Edge, Brave, Arc, Opera, Vivaldi, etc.)
• Claude Code v2.1.80+ (the recorder needs channels; browser automation alone works on v2.0.73+)
• An OpenAI API key (used to transcribe recording narration)

Step 1: Install dependencies

npm install --prefix host
npm install --prefix host/codemode/worker

The second one is not optional: it provisions the sandbox that execute_code runs in. Skip it and the server falls back to fetching wrangler over the network on every cold start, which is the most common reason execute_code fails to come up.

Step 2: Load the extension

1. Go to chrome://extensions (or brave://extensions / edge://extensions)
2. Enable Developer mode
3. Click Load unpacked and select the extension/ directory
4. Copy the extension ID shown under the extension name

Step 3: Register native messaging

./install.sh <your-extension-id>

If you use multiple browsers, pass all IDs: ./install.sh <chrome-id> <brave-id> <arc-id>

Step 4: Restart your browser

Close all windows and reopen. The browser reads native messaging host configs on startup.

Step 5: Set your OpenAI key and enable the microphone

Right-click the extension icon → Options. Both of these are required before recording:

• Paste your OpenAI key and click Save & validate (transcribes your narration).
• Click Enable microphone and allow the browser prompt. The recorder captures audio in a background page that can't show a permission prompt itself, so you grant mic access once here; otherwise recordings capture no voice.

Step 6: Add the server to Claude Code

The hybrid server exposes everything: all 21 tools directly, execute_code alongside (the model picks per call), and the recording channel.

claude mcp add open-claude-in-chrome-hybrid -- node /absolute/path/to/host/codemode/server-hybrid.js

Find the absolute path with echo "$(pwd)/host".

Step 7: Launch with recording enabled

Channels are a research preview, so start Claude Code with the development flag (the name is the server from step 6):

claude --dangerously-load-development-channels server:open-claude-in-chrome-hybrid

Accept the one-time prompt and keep the session open — channels inject into a live interactive session, not claude -p. That's it: browser automation and recording are both on.

Verification

Start a new Claude Code session and run both checks.

1. Browser control — confirms the extension, native host and MCP server are wired up:

Navigate to reddit.com and take a screenshot

Reddit loads. No domain restriction.

2. The execute_code sandbox — confirms the wrangler sidecar is live:

In a single execute_code call: create a new tab, navigate to reddit.com, click
the first post, then go back to the listing and give me every post title except
the top three.

You should get the titles back from one tool call rather than a click-screenshot-click sequence. If the first attempt reports the sandbox is still starting, wait a few seconds and ask again — the sidecar boots in the background and the first call can arrive before it is ready. If it never comes up, see Keeping execute_code running.