debug-bridge

Debug Bridge Runbook

Control web apps via WebSocket. Click, type, screenshot, inspect, capture network traffic, monitor navigation.

Prerequisites (Webapp Setup)

The webapp MUST have the debug-bridge SDK installed and configured before agents can control it.

Step 1: Install SDK in Webapp

npm install debug-bridge-browser

Step 2: Add Initialization Code

Create src/debug-bridge.ts (or add to your app's entry point):

import { createDebugBridge } from 'debug-bridge-browser';

// ONLY runs in development - safe to leave in production builds
if (import.meta.env.DEV) {
  const params = new URLSearchParams(window.location.search);
  const session = params.get('session');
  const port = params.get('port') || '4000';

  if (session) {
    const bridge = createDebugBridge({
      url: `ws://localhost:${port}/debug?role=app&sessionId=${session}`,
      sessionId: session,
      appName: 'My App',  // Shows in CLI when connected
      appVersion: '1.0.0',

      // Feature toggles (all true by default)
      enableNetwork: true,      // Capture fetch/XHR requests
      enableNavigation: true,   // Track route changes
      enableConsole: true,      // Capture console.log/error
      enableErrors: true,       // Capture unhandled errors

      // Optional: filter which URLs to capture
      networkUrlFilter: (url) => !url.includes('/analytics'),
      maxNetworkBodySize: 10000,  // Truncate large request/response bodies
    });

    bridge.connect();

    // Optional: expose for manual debugging
    (window as any).__debugBridge = bridge;
  }
}

Step 3: Import in App Entry

// main.tsx or App.tsx
import './debug-bridge';  // Add this import

How It Works

1. Webapp reads ?session=X&port=Y from URL
2. If present, connects to debug server as role=app
3. Agent connects to same server as role=agent
4. Agent sends commands → Server relays → Webapp executes → Results returned

┌─────────────┐     WebSocket      ┌─────────────┐     WebSocket      ┌─────────────┐
│   AI Agent  │ ◄─────────────────► │  CLI Server │ ◄─────────────────►│   Webapp    │
│             │   role=agent       │  (port 4000) │   role=app         │  (browser)  │
└─────────────┘                    └─────────────┘                    └─────────────┘

---

Agent Usage

Once the webapp has the SDK configured, agents can control it.

Quick Start

# 1. Start debug server (in tmux for persistence)
SESSION="debug-$(date +%s)"
PORT=$(shuf -i 4000-4999 -n 1)
tmux new-session -d -s "$SESSION"
tmux send-keys -t "$SESSION" "npx debug-bridge-cli connect --session $SESSION --port $PORT 2>&1 | tee debug-bridge-$PORT.log" C-m

# 2. Open webapp with debug params (webapp must have SDK installed!)
open "http://localhost:5173?session=$SESSION&port=$PORT"

# 3. Attach to tmux to use CLI
tmux attach -t "$SESSION"

CLI Commands

Command	Example	Description
ui	ui	List interactive elements
click <target>	click 3 or click "Sign In"	Click element
type <target> <text>	type 1 "hello" or type "email" "[email protected]"	Type into input
js <code>	js document.title	Run JavaScript, shows result
screenshot	screenshot	Save viewport as PNG
state	state	Get cookies, localStorage
go <url>	go /login	Navigate to URL
find <query>	find email	Search UI tree
eval <code>	eval localStorage.clear()	Alias for js
help	help	Show all available commands

AI Agent Usage (via tmux)

AI agents can't attach to terminals interactively. Use tmux send-keys to send commands and tmux capture-pane to read output:

# Send a command to the debug-bridge CLI
tmux send-keys -t "$SESSION" "screenshot" C-m

# Wait for result and read output
sleep 2
tmux capture-pane -t "$SESSION" -p | tail -20

# Run JavaScript in the browser
tmux send-keys -t "$SESSION" "js document.title" C-m
sleep 1
tmux capture-pane -t "$SESSION" -p | tail -5

# Trigger events (e.g., for testing visibility handlers)
tmux send-keys -t "$SESSION" 'eval window.dispatchEvent(new Event("focus"))' C-m

Key Pattern for AI Agents:

1. Start CLI in tmux (not foreground)
2. Send commands via tmux send-keys
3. Read results via tmux capture-pane
4. Screenshots are saved as PNG files in current directory

Targeting Elements

Elements can be targeted by:

• Index: click 3 (element #3 from ui output)
• Text: click "Submit" (matches button/link text)
• Placeholder: type "email" "[email protected]"
• StableId: click btn-656b07 (hash shown in ui output)

WebSocket API (Programmatic)

// Connect as agent
const ws = new WebSocket(`ws://localhost:4000/debug?role=agent&sessionId=my-session`);

// Base message (required fields)
const msg = {
  protocolVersion: 1,
  sessionId: 'my-session',
  timestamp: Date.now(),
  requestId: crypto.randomUUID()
};

// Send commands
ws.send(JSON.stringify({ ...msg, type: 'request_ui_tree' }));
ws.send(JSON.stringify({ ...msg, type: 'click', target: { stableId: 'btn-abc' } }));
ws.send(JSON.stringify({ ...msg, type: 'type', target: { selector: '#email' }, text: '[email protected]' }));
ws.send(JSON.stringify({ ...msg, type: 'evaluate', code: 'document.title' }));
ws.send(JSON.stringify({ ...msg, type: 'request_screenshot' }));
ws.send(JSON.stringify({ ...msg, type: 'navigate', url: '/dashboard' }));

Response Types

// UI Tree response
{ type: 'ui_tree', items: [{ stableId, role, text, label, visible, meta }] }

// Command success
{ type: 'command_result', success: true, result: any, duration: 5 }

// Screenshot
{ type: 'screenshot', data: 'base64...', width: 1920, height: 1080 }

// Error
{ type: 'command_result', success: false, error: { code: 'TARGET_NOT_FOUND', message: '...' } }

// Network request (auto-streamed)
{ type: 'network_request', requestId: 'net-1-1234', method: 'POST', url: '/api/users', initiator: 'fetch' }

// Network response (auto-streamed)
{ type: 'network_response', requestId: 'net-1-1234', status: 200, statusText: 'OK', duration: 45, ok: true, body: '{"id":1}' }

// Navigation event (auto-streamed)
{ type: 'navigation', url: '/dashboard', previousUrl: '/login', trigger: 'pushstate' }

// Console message (auto-streamed)
{ type: 'console', level: 'error', args: ['Failed to fetch user', '{"status":401}'] }

---

Example Workflows

Login Flow

ui                           # Discover form elements
type "email" "[email protected]" # Fill email field
type "password" "secret123"  # Fill password field
click "Sign In"              # Click submit button
screenshot                   # Capture result for verification

Form Testing

go /register                 # Navigate to page
ui                           # List interactive elements
type 1 "John"                # Fill first input by index
type 2 "[email protected]"       # Fill second input
click "Submit"               # Submit form
state                        # Check localStorage for saved data

Debugging

ui                           # See current page state
js localStorage.getItem('token')  # Check auth token
js window.__REDUX_STATE__    # Inspect app state
screenshot                   # Capture for analysis

API Debugging (Network Capture)

# Network requests are auto-captured - watch the CLI output:
# 🌐 [POST] /api/login
#    ✓ 200 OK (45ms)
# 🌐 [GET] /api/users/me
#    ✗ 401 Unauthorized (12ms)

# Navigation is also tracked:
# 🔀 [pushstate] /dashboard
# 🔀 [popstate] /login

Monitoring API Calls

// Connect as agent and filter for network events
ws.onmessage = (e) => {
  const msg = JSON.parse(e.data);
  if (msg.type === 'network_response' && !msg.ok) {
    console.log(`API Error: ${msg.status} on request ${msg.requestId}`);
  }
  if (msg.type === 'navigation') {
    console.log(`User navigated to: ${msg.url}`);
  }
};

---

Error Recovery

Error	Cause	Fix
TARGET_NOT_FOUND	Element not in DOM	Run ui to refresh, verify element exists
TARGET_NOT_VISIBLE	Element off-screen	scroll 0 500 first, then retry
EVAL_DISABLED	App disabled eval	Use DOM commands instead
SCREENSHOT_FAILED	Modern CSS (oklch)	Use js to inspect DOM directly
No connection	Webapp missing SDK	Verify SDK is installed and initialized
Missing network events	SDK config	Check enableNetwork: true in config
Missing navigation events	SDK config	Check enableNavigation: true in config

Telemetry Reference

Telemetry	Auto-sent	Description
ui_tree	On connect + changes	Interactive elements list
dom_mutations	Continuous	DOM changes (batched)
console	Continuous	Console.log/warn/error
error	On error	Unhandled errors
network_request	On fetch/XHR	Outgoing API calls
network_response	On response	API responses with status/body
navigation	On route change	URL changes (push/pop/replace/hash)
state_update	On change	Custom app state (if configured)

Troubleshooting

# Port already in use
lsof -ti:4000 | xargs kill -9

# Check if server is running
tmux attach -t debug-*

# View server logs
tail -f debug-bridge-*.log

# Webapp not connecting?
# 1. Check URL has ?session=X&port=Y
# 2. Check browser console for [DebugBridge] logs
# 3. Verify SDK is imported in dev mode