blue/.blue/docs/spikes/2026-01-30T1711Z-playwright-mcp-multiple-window-isolation.wip.md

Spike: Playwright MCP Multiple Window Isolation Issue

Status	WIP
Created	2026-01-30
Category	Tooling / MCP Integration

---

Problem Statement

When more than one Chrome window is open, the Playwright MCP:

1. Opens a new tab in an existing window
2. Cannot subsequently find/control that tab
3. Results in "tab not found" or stale reference errors

This blocks verification workflows and browser automation tasks.

---

Root Cause Analysis

Primary Cause: Extension Mode Single-Tab Limitation

When Playwright MCP runs in extension mode (connecting via browser extension to an existing Chrome instance), it operates with single-tab scope for security:

• Extension opens a new tab when establishing connection
• Extension can only control one tab at a time
• Tabs in different windows are logically separate in the extension's scope
• Extension doesn't maintain cross-window tab references

Contributing Factor: Browser Context Isolation

Playwright uses isolated browser contexts by default:

• Each window may have its own context scope in CDP (Chrome DevTools Protocol)
• Creating a tab in one window doesn't register in another window's context
• Session tracking is per-connection, not per-browser-instance

Contributing Factor: No Global Tab Registry

The MCP server lacks a global tab registry:

• Tab selection defaults to active window only
• browser_tabs calls don't search across all windows
• New tabs exist but can't be found (different window context)

---

Solutions Analysis

Solution 1: Disable Extension Mode (Recommended)

Feasibility: High | Effort: Minimal | Risk: Low

Launch Playwright MCP with its own browser instance instead of connecting via extension.

Implementation:

// In MCP config, remove or set to false:
{
  "playwright": {
    "extension": false
  }
}

Trade-offs:

• (+) Eliminates single-tab limitation
• (+) Full control over tabs and windows
• (+) Immediate fix, no code changes
• (-) Loses logged-in sessions (requires re-authentication)
• (-) Slightly longer startup time

Solution 2: CDP Direct Connection

Feasibility: Medium | Effort: Low-Medium | Risk: Medium

Use Chrome DevTools Protocol direct connection instead of extension mode.

Implementation:

# Launch Chrome with CDP enabled
/Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome \
  --remote-debugging-port=9222

# Configure Playwright MCP
export PLAYWRIGHT_MCP_BROWSER_ENDPOINT="http://localhost:9222"

Trade-offs:

• (+) Better than extension mode for multi-window
• (+) Uses existing Chrome instance
• (-) Requires manual Chrome startup with flags
• (-) May still have context isolation at protocol level

Solution 3: Persistent Browser Profile Mode

Feasibility: Medium | Effort: Low-Medium | Risk: Medium

Use Playwright MCP with a dedicated, persistent browser profile.

Implementation:

/Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome \
  --user-data-dir=$HOME/.playwright-profiles/mcp-profile \
  --remote-debugging-port=9222

Trade-offs:

• (+) Maintains authentication state across sessions
• (+) Supports multiple tabs/windows
• (-) Separate profile from main browser
• (-) Initial auth setup required

Solution 4: Blue MCP Tab Registry (Future)

Feasibility: Lower | Effort: High | Risk: High

Implement a tab registry in Blue MCP that tracks tabs across windows.

// Hypothetical handler
struct TabRegistry {
    tabs: HashMap<String, TabInfo>,  // tab_id -> (window_id, context_id, url)
    current_window: Option<String>,
}

Trade-offs:

• (+) Solves at Blue layer, works with any Playwright config
• (+) Enables future features (tab memory, session persistence)
• (-) Significant development effort
• (-) Must track Playwright MCP changes

---

Recommendation

Immediate: Use Solution 1 (disable extension mode)

• Zero code changes
• Reliable multi-window support
• Only cost is one-time re-authentication

If logged-in sessions are critical: Use Solution 3 (persistent profile)

• Maintains auth across sessions
• Isolated from personal browsing

Long-term consideration: Solution 4 if Blue needs deeper browser automation control.

---

Diagnostic Commands

To identify which mode is active:

# Check Claude MCP config for extension mode
cat ~/.claude/settings.json | grep -A5 playwright

# Check if CDP port is in use
lsof -i :9222

---

References

• microsoft/playwright-mcp - GitHub
• Browser Context Management | DeepWiki
• Issue #1111 - Close tabs not working with extension
• Issue #1144 - Tab Access across windows
• Issue #1036 - Allow selection of target tab session

---

Next Steps

• Verify current Playwright MCP configuration
• Test Solution 1 (disable extension mode)
• Document authentication workflow if re-auth needed
• Update project MCP config if change is accepted