A dedicated Chrome for chrome-devtools-mcp that can sign in

Letting chrome-devtools-mcp (the MCP server that drives a browser for Claude Code, Cursor, VS Code...) launch Chrome itself causes three problems: Google and Cloudflare block sign-in, two projects opening a browser at once collide, and the agent can see every tab in your personal Chrome. This guide sets up a dedicated Chrome profile per project so the MCP attaches only to that browser, can still sign in and keep the session, and runs several projects in parallel.

Throughout, <profiles-root> is the folder that holds your profiles (for example %USERPROFILE%\chrome-mcp-profiles), and <project-slug> is a project's short name (lowercase, digits, hyphens). Verified on Windows 11 + Chrome stable 153 + chrome-devtools-mcp 1.9.0; the idea applies to other MCP clients too.

The problem with the default setup

When .mcp.json declares chrome-devtools-mcp with no flags, the MCP launches Chrome with Puppeteer using one profile shared across every project. Four consequences:

Comparing the launch methods

The crux: when the MCP launches Chrome it always adds an automation flag (sign-in blocked); when you launch Chrome yourself and the MCP only CONNECTS, that flag is absent.

The last row is this guide's goal. You open Chrome with a launcher (no automation flag), and the MCP just reads that folder's debug port and attaches.

Why Chrome allows the debug port on a dedicated profile

Since Chrome 136, --remote-debugging-port and --remote-debugging-pipe are ignored on the default data directory; to use them you must add --user-data-dir pointing to a different directory. The reason: since App-Bound Encryption shipped, attackers have used remote debugging to steal cookies, so Chrome closes that path on the default profile.

Why sign-in is blocked, and how to avoid it legitimately

Google/Cloudflare block when they see navigator.webdriver === true. That property is true whenever any control signal is present:

So you cannot sign in while a debug port is open. The legitimate workaround (no spoofing tricks) is to split two modes over the same data directory:

• Login mode: open Chrome with NO debug port and no automation flag. You sign in to Google/Cloudflare like a normal browser. Cookies are saved into the profile folder.
• Work mode: fully close that Chrome, reopen it WITH --remote-debugging-port=0. The MCP attaches. The cookies from the login are still there, so pages keep the session - and now you do not need to sign in again.

How it works

Your main Chrome                Project A's Chrome                Project B's Chrome
(default profile, no port)      <profiles-root>\A                 <profiles-root>\B
        ^                       --remote-debugging-port=0         --remote-debugging-port=0
        |                              | writes                          | writes
  no MCP attaches here          A\DevToolsActivePort (random port)       B\DevToolsActivePort
                                       ^ reads                          ^ reads
                               Project A's MCP                    Project B's MCP
                               --autoConnect                      --autoConnect
                               --userDataDir=<...>\A              --userDataDir=<...>\B

The detailed flow:

1. The launcher runs chrome.exe --user-data-dir="<profiles-root>\<slug>" --no-first-run --no-default-browser-check --remote-debugging-port=0.
2. Chrome picks a free port and writes <folder>\DevToolsActivePort with two lines: the port number and a /devtools/browser/<uuid> path. The port listens on 127.0.0.1 only.
3. With --autoConnect, the MCP reads DevToolsActivePort inside the exact --userDataDir folder, builds ws://127.0.0.1:<port><path> and connects. If the file is missing or the port does not answer, the MCP reports Could not connect to Chrome in <folder> and does NOT launch a browser of its own.
4. When the MCP session ends, the MCP only disconnects - Chrome stays open.

Setting up a project

1. Create the root folder <profiles-root> (e.g. %USERPROFILE%\chrome-mcp-profiles) and put the launcher open-chrome-mcp.ps1 (code below) in it.
2. Choose <project-slug> matching ^[a-z0-9][a-z0-9-]*$, one slug per project.
3. Create the two .cmd files in the project root (code below), substituting <project-slug> and the launcher path.
4. Edit the project's .mcp.json: point the chrome-devtools entry's --autoConnect --userDataDir at <profiles-root>\<project-slug>.
5. Sign in (if the project needs accounts): run login mode, sign in, fully close it.
6. Open work mode, then restart the MCP client so it loads the new .mcp.json.

The code

Launcher open-chrome-mcp.ps1

Put it in <profiles-root>. Save it as UTF-8 with BOM (PowerShell 5.1 reads a BOM-less file as ANSI, mangling non-ASCII text). The script locates its own folder, so it holds no absolute paths.

param(
    [Parameter(Mandatory = $true)]
    [ValidatePattern('^[a-z0-9][a-z0-9-]*$')]
    [string]$Project,
    [switch]$Login
)

$ErrorActionPreference = 'Stop'
$profileDir = Join-Path $PSScriptRoot $Project     # <profiles-root>\<Project>
$portFile   = Join-Path $profileDir 'DevToolsActivePort'

$chrome = @(
    "$env:ProgramFiles\Google\Chrome\Application\chrome.exe",
    "${env:ProgramFiles(x86)}\Google\Chrome\Application\chrome.exe",
    "$env:LOCALAPPDATA\Google\Chrome\Application\chrome.exe"
) | Where-Object { Test-Path $_ } | Select-Object -First 1
if (-not $chrome) { Write-Host 'Google Chrome not found.' -ForegroundColor Red; exit 1 }

# Chrome allows only one process per data directory. If a Chrome is already running on this
# folder, a new launch IGNORES the flags you pass -> check first so we do not open the wrong mode.
function Test-ProfileChromeRunning {
    $needle = "--user-data-dir=`"$profileDir`"".ToLowerInvariant()
    [bool](Get-CimInstance Win32_Process -Filter "Name='chrome.exe'" |
        Where-Object { $_.CommandLine -and $_.CommandLine.ToLowerInvariant().Contains($needle) })
}

# Return the port if the debug port in DevToolsActivePort answers, otherwise $null.
function Get-LiveDebugPort {
    try {
        if (-not (Test-Path $portFile)) { return $null }
        $port = (Get-Content $portFile -TotalCount 1).Trim()
        if (-not $port) { return $null }
        Invoke-RestMethod "http://127.0.0.1:$port/json/version" -TimeoutSec 2 | Out-Null
        return $port
    } catch { return $null }
}

if (Test-ProfileChromeRunning) {
    $port = Get-LiveDebugPort
    if ($Login) {
        if ($port) { Write-Host "Already open in work mode (port $port). Close it fully, then retry." -ForegroundColor Yellow; exit 1 }
        Write-Host 'Already open in login mode.' -ForegroundColor Green; exit 0
    }
    if ($port) { Write-Host "Ready for the MCP (port $port)." -ForegroundColor Green; exit 0 }
    Write-Host 'Open but no debug port (login mode). Close it fully, then retry.' -ForegroundColor Yellow
    exit 1
}

New-Item -ItemType Directory -Force $profileDir | Out-Null
$chromeArgs = @("--user-data-dir=`"$profileDir`"", '--no-first-run', '--no-default-browser-check')
if (-not $Login) {
    Remove-Item $portFile -Force -ErrorAction SilentlyContinue  # drop the previous run's stale port
    $chromeArgs += '--remote-debugging-port=0'
}
Start-Process -FilePath $chrome -ArgumentList $chromeArgs

if ($Login) {
    Write-Host 'Opened in login mode. Sign in, close it fully, then reopen work mode.' -ForegroundColor Green
    exit 0
}

for ($i = 0; $i -lt 40; $i++) {
    $port = Get-LiveDebugPort
    if ($port) { Write-Host "Opened for the MCP (port $port, local only)." -ForegroundColor Green; exit 0 }
    Start-Sleep -Milliseconds 250
}
Write-Host 'Opened but no debug port after 10 seconds.' -ForegroundColor Red
exit 1

The project's two double-click files

Put them in the project root, keep the contents ASCII (cmd reads batch files in the OEM code page). Substitute <project-slug> and the launcher path.

open-chrome-for-mcp.cmd (work mode):

@echo off
rem Opens this project's dedicated Chrome in work mode (random remote-debugging port)
rem so chrome-devtools-mcp (--autoConnect --userDataDir) can attach to it.
powershell -NoProfile -ExecutionPolicy Bypass -File "%USERPROFILE%\chrome-mcp-profiles\open-chrome-mcp.ps1" -Project <project-slug>
if errorlevel 1 (pause) else (timeout /t 4 >nul)

open-chrome-for-mcp-login.cmd (login mode):

@echo off
rem Opens this project's dedicated Chrome in login mode (NO debug port) so Google / Cloudflare
rem sign-in behaves like a normal browser. Sign in, close that Chrome fully, then run
rem open-chrome-for-mcp.cmd. Cookies stay in the profile folder.
powershell -NoProfile -ExecutionPolicy Bypass -File "%USERPROFILE%\chrome-mcp-profiles\open-chrome-mcp.ps1" -Project <project-slug> -Login
if errorlevel 1 (pause) else (timeout /t 6 >nul)

-ExecutionPolicy Bypass applies only to that PowerShell process; it does not change any system setting.

The chrome-devtools entry in .mcp.json

JSON does not expand environment variables, so use an absolute path. In JSON, \ is \\.

{
  "mcpServers": {
    "chrome-devtools": {
      "command": "cmd",
      "args": [
        "/c", "npx", "-y", "[email protected]",
        "--autoConnect",
        "--userDataDir=<profiles-root>\\<project-slug>"
      ]
    }
  }
}

Day-to-day use

While the agent works, you keep using your main Chrome normally. Pick a distinct theme color for this Chrome so it is easy to tell apart.

Security

• While the dedicated Chrome is in work mode, any program on the machine can connect to the debug port (it listens on 127.0.0.1 only, not the network) and control that Chrome, including reading cookies. So: only sign in to the accounts a project truly needs, and close the dedicated Chrome when done.
• Keep chrome://inspect/#remote-debugging OFF on your main Chrome - it is the one remaining way to open a debug port on the default profile.
• The <profiles-root>\<slug> folder holds login cookies. Do not commit it, sync it to the cloud, or share it.
• Consider extra flags: --redactNetworkHeaders (hide sensitive headers when reading network traffic), --allowedUrlPattern / --blockedUrlPattern (limit which pages the MCP may open).

Troubleshooting

References

• Chrome for Developers - Changes to remote debugging switches (Chrome 136): https://developer.chrome.com/blog/remote-debugging-port
• chrome-devtools-mcp - Advanced usage (--autoConnect, --browser-url, debug-port security warning): https://github.com/ChromeDevTools/chrome-devtools-mcp/blob/main/docs/advanced-usage.md
• Connect your AI agent to your personal browser with auto-connect (Chrome 144+): https://developer.chrome.com/docs/devtools/agents/use-cases/auto-connect
• MDN - Navigator: webdriver property: https://developer.mozilla.org/en-US/docs/Web/API/Navigator/webdriver