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
bash
npm install debug-bridge-browser
Step 2: Add Initialization Code
Create src/debug-bridge.ts (or add to your app's entry point):
typescript
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
typescript
// main.tsx or App.tsx import './debug-bridge'; // Add this import
How It Works
- •Webapp reads
?session=X&port=Yfrom URL - •If present, connects to debug server as
role=app - •Agent connects to same server as
role=agent - •Agent sends commands → Server relays → Webapp executes → Results returned
code
┌─────────────┐ 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
bash
# 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 "$SESSION"
CLI Commands
| Command | Example | Description |
|---|---|---|
ui | ui | List interactive elements |
click <target> | click 3 or click "Sign In" | Click element |
type <target> <text> | type 1 "hello" or type "email" "a@b.com" | Type into input |
js <code> | js document.title | Run JavaScript, shows result |
screenshot | screenshot | Save viewport as PNG |
state | state | Get cookies, localStorage |
go <url> | go /login | Navigate to URL |
find <query> | find email | Search UI tree |
eval <code> | eval localStorage.clear() | Alias for js |
help | help | Show all available commands |
AI Agent Usage (via tmux)
AI agents can't attach to terminals interactively. Use tmux send-keys to send commands and tmux capture-pane to read output:
bash
# Send a command to the debug-bridge CLI
tmux send-keys -t "$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:
- •Start CLI in tmux (not foreground)
- •Send commands via
tmux send-keys - •Read results via
tmux capture-pane - •Screenshots are saved as PNG files in current directory
Targeting Elements
Elements can be targeted by:
- •Index:
click 3(element #3 fromuioutput) - •Text:
click "Submit"(matches button/link text) - •Placeholder:
type "email" "test@example.com" - •StableId:
click btn-656b07(hash shown inuioutput)
WebSocket API (Programmatic)
javascript
// 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: 'test@example.com' }));
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
javascript
// 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
code
ui # Discover form elements type "email" "user@test.com" # Fill email field type "password" "secret123" # Fill password field click "Sign In" # Click submit button screenshot # Capture result for verification
Form Testing
code
go /register # Navigate to page ui # List interactive elements type 1 "John" # Fill first input by index type 2 "john@test.com" # Fill second input click "Submit" # Submit form state # Check localStorage for saved data
Debugging
code
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)
code
# 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
javascript
// 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
bash
# 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