ClawBench Chrome Extension

June 13, 2026 · View on GitHub

This is the source code for the ClawBench Chrome Extension, which provides browser fingerprint hardening for benchmark runs.

The extension is responsible for the following tasks:

Injecting stealth.js at document_start in the page's MAIN world.
Applying anti-bot-detection patches for webdriver, plugins, WebGL, permissions, and related browser fingerprints.

Action capture, screenshot capture, request logging, request interception, and tab activation are handled by the runtime server over CDP. The extension does not send data to the server.

A setup.sh script is provided to load the extension into Chrome. Linux and macOS are supported.

Files

File	Description
`manifest.json`	Manifest V3 extension definition. Loads `stealth.js` on all URLs.
`stealth.js`	Anti-bot-detection patches. Runs at `document_start` in `MAIN` world. Overrides `navigator.webdriver`, plugins, WebGL, permissions, etc.
`setup.sh`	Detects Chrome/Chromium binary on macOS or Linux and launches with `--load-extension` and remote debugging enabled.

Event Capture

Browser event capture now lives in src/clawbench/runtime/runtime-server/server.py. The server injects capture listeners through CDP and preserves the historical action schema:

click, keydown, keyup, input, scroll, change, submit, plus a synthetic pageLoad on each navigation.

Throttling

High-frequency events (scroll, input) are throttled to one every 500ms. Screenshots are also throttled to one every 500ms.

Action Payload

Each action sent to the server contains:

{
  "type": "click",
  "timestamp": 1710000001234,
  "url": "https://example.com/",
  "target": {
    "tagName": "BUTTON",
    "id": "submit-btn",
    "className": "btn primary",
    "textContent": "Submit",
    "xpath": "/html[1]/body[1]/form[1]/button[1]"
  },
  "x": 255,
  "y": 245
}

Additional fields by event type:

click: x, y (coordinates)
keydown/keyup: key (key name)
input/change: value (truncated to 200 chars)
scroll: scrollX, scrollY
pageLoad: title

The extension includes stealth.js, a content script injected at document_start in the MAIN world — meaning it runs before any page JavaScript and patches the page's actual window/navigator objects (not the extension's isolated world). This reduces the chance of being blocked by reCAPTCHA, Cloudflare Turnstile, and similar bot-detection systems.

The stealth measures are split across three layers:

Layer 1: Chrome Launch Flags (`entrypoint.sh`)

Flag	What it does
Removed `--enable-automation`	Was explicitly telling Chrome to set `navigator.webdriver = true` and show the "controlled by automated software" infobar. Removing it eliminates both signals.
Removed `--disable-gpu`	Was disabling all GPU/WebGL rendering. Sites that fingerprint WebGL would see no renderer — a strong headless signal.
`--disable-blink-features=AutomationControlled`	Tells Blink not to set `navigator.webdriver = true`, even if CDP is attached. Belt-and-suspenders with the flag removal.
`--use-gl=angle --use-angle=swiftshader`	Enables software-rendered WebGL via SwiftShader through the ANGLE backend. This makes WebGL available with realistic renderer strings without a real GPU. Trade-off: higher CPU usage since all GL operations run in software.
`--enable-webgl`	Explicitly ensures WebGL contexts can be created.
`--remote-debugging-address=127.0.0.1`	CDP was previously bound to `0.0.0.0` (all interfaces). Now only accessible internally. External access still works through the `socat` forwarder on port 9223. Prevents page JavaScript from detecting CDP by probing network ports.

Layer 2: Chrome Profile (`entrypoint.sh`)

An empty Chrome profile with no bookmarks, no history, and no preferences is a strong signal of a freshly-created automated browser. The entrypoint now pre-populates:

Preferences: accept_languages, safebrowsing, dns_prefetching, window_placement, skip_first_run_ui, etc.
Bookmarks: Three common entries (Google, YouTube, Wikipedia).
Local State: Profile metadata with a named profile ("Person 1").

Layer 3: JavaScript Patches (`stealth.js`)

#	Patch	Why
1	`navigator.webdriver → false`	The #1 bot detection signal. Real Chrome returns `false`; automated Chrome returns `true`. Even with the Blink flag, CDP attachment can re-enable it.
2	`navigator.languages → ['en-US', 'en']`	Ensures consistent locale regardless of container environment.
3	`navigator.plugins` — fake Chrome PDF Plugin, Chrome PDF Viewer, Native Client	Headless/automated Chrome reports an empty `PluginArray` (length 0). Real Chrome always has PDF and NaCl plugins.
4	`navigator.mimeTypes` — fake `application/pdf` entries	Must match the fake plugins. Empty mimeTypes = headless signal.
5	WebGL `getParameter()` — return SwiftShader vendor/renderer	Even with SwiftShader actually running, this ensures consistent, known-good strings across Chromium versions. Intercepts `UNMASKED_VENDOR_WEBGL` (0x9245) and `UNMASKED_RENDERER_WEBGL` (0x9246).
6	`Permissions.query({name:'notifications'})` → `'prompt'`, `Notification.permission` → `'default'`	Automated browsers deny all permissions by default. Real browsers return `'prompt'`/`'default'` for notifications.
7	`window.chrome.runtime` — ensure object exists	Some bot detectors check `if (!window.chrome \|\| !window.chrome.runtime)` to distinguish headless Chrome from real Chrome.
8	Remove `$cdc_`/`cdc_` properties on `document`	Chromedriver injects these properties. Not used by CDP directly, but removed as a precaution.
9	`navigator.hardwareConcurrency` → 8 (if < 4)	Docker containers with limited CPUs may report 1-2, which is suspicious for a desktop browser.
10	`navigator.deviceMemory` → 8 (if < 4)	Same — low memory is suspicious for desktop.
11	Iframe `navigator.webdriver` patching	Advanced fingerprinters create iframes and check `navigator.webdriver` inside them to bypass page-level overrides. We hook `document.createElement('iframe')` and patch the iframe's navigator on load.

Layer 4: Dockerfile

libegl1 and libgbm1 are installed to provide the EGL and GBM libraries that Chrome's ANGLE/SwiftShader backend needs. Without them, --use-gl=angle silently falls back to no-GPU mode.

Test Results

Verified against bot-detection sites (2026-03-28):

Test	Result
bot.sannysoft.com	10/11 main tests pass (only "WebDriver New" orange — CDP attachment quirk; "WebDriver Advanced" passes)
intoli headless detection	"You are not Chrome headless"
Cloudflare (nowsecure.nl)	Soft Turnstile challenge (not hard-blocked)
CreepJS	Fingerprint generated without bot flag

Local Development

Run Chrome with the extension loaded:

./setup.sh https://example.com