Headless Browser Detection: How to Catch Playwright, Puppeteer, and Selenium Bots

The bot detection arms race has evolved. Simple user-agent checks and IP blocklists don’t work anymore. Modern attackers use headless browsers—automated browser instances that execute JavaScript, render pages, and mimic human behavior.

Playwright, Puppeteer, and Selenium are the weapons of choice. They can bypass CAPTCHAs, defeat fingerprinting, and automate attacks at scale. Worse, stealth plugins make them nearly indistinguishable from real browsers.

This guide covers the techniques that actually work for detecting headless browsers in 2025.

Understanding Headless Browsers

What Is a Headless Browser?

A headless browser is a web browser without a graphical user interface. It runs programmatically, executing JavaScript and rendering pages just like a regular browser—but controlled by automation scripts instead of a human.

Common headless browser tools:

Why Attackers Use Headless Browsers

Traditional HTTP-based bots are easy to detect—they don’t execute JavaScript, load assets, or maintain sessions properly. Headless browsers solve these problems:

• JavaScript execution - Pass JS-based bot challenges
• Full DOM rendering - Interact with dynamic content
• Cookie handling - Maintain sessions across requests
• Browser APIs - Access navigator, window, document objects
• Screenshot capability - Solve visual CAPTCHAs with AI
• Network interception - Modify requests and responses

The result: Headless browsers look nearly identical to real browsers at the protocol level.

The Stealth Problem

Basic headless detection got harder with stealth plugins:

• puppeteer-extra-plugin-stealth - Patches 10+ detection vectors
• playwright-stealth - Port of stealth techniques for Playwright
• undetected-chromedriver - Modified ChromeDriver that avoids detection
• selenium-stealth - Stealth patches for Selenium

These plugins modify browser properties to match real browsers, hide automation indicators, and spoof fingerprints.

But they’re not perfect. Let’s explore what still works.

Detection Techniques That Work

1. Navigator Property Analysis

Headless browsers expose themselves through subtle differences in the navigator object.

webdriver property:

The most basic check—automation tools set navigator.webdriver = true:

if (navigator.webdriver === true) {
  // Definitely automation
  flagAsBot();
}

Stealth bypass: Most stealth plugins delete this property. But the deletion itself can be detected:

// Check if webdriver was deleted (not naturally absent)
const hasWebdriver = 'webdriver' in navigator;
const webdriverValue = navigator.webdriver;

if (hasWebdriver && webdriverValue === undefined) {
  // Property exists but was set to undefined (stealth plugin)
  flagAsSuspicious();
}

plugins and mimeTypes:

Real browsers have plugins (PDF viewer, etc.). Headless browsers often have empty or inconsistent plugin lists:

const plugins = navigator.plugins;
const mimeTypes = navigator.mimeTypes;

if (plugins.length === 0 || mimeTypes.length === 0) {
  flagAsSuspicious();
}

// Check for realistic plugin patterns
const hasChromePDF = Array.from(plugins).some(p =>
  p.name.includes('Chrome PDF')
);
if (!hasChromePDF && navigator.userAgent.includes('Chrome')) {
  flagAsSuspicious();
}

languages consistency:

Check that language settings are consistent:

const languages = navigator.languages;
const language = navigator.language;

if (!languages || languages.length === 0) {
  flagAsSuspicious();
}

if (languages[0] !== language) {
  flagAsSuspicious();
}

2. Chrome Object Detection

Real Chrome browsers expose a window.chrome object with specific properties.

// Check for chrome object
if (!window.chrome) {
  flagAsSuspicious();
}

// Check for chrome.runtime (present in real Chrome)
if (!window.chrome.runtime) {
  flagAsSuspicious();
}

// Check for chrome.csi (Chrome-specific timing)
if (typeof window.chrome.csi !== 'function') {
  flagAsSuspicious();
}

// Check for chrome.loadTimes (deprecated but still present)
if (typeof window.chrome.loadTimes !== 'function') {
  flagAsSuspicious();
}

Stealth bypass: Plugins mock the chrome object, but often imperfectly:

// Deep inspection of chrome object
const chromeKeys = Object.keys(window.chrome || {});
const expectedKeys = ['app', 'csi', 'loadTimes', 'runtime'];

const missingKeys = expectedKeys.filter(k => !chromeKeys.includes(k));
if (missingKeys.length > 2) {
  flagAsSuspicious();
}

3. Permission API Inconsistencies

Real browsers have consistent permission states. Headless browsers often don’t:

async function checkPermissions() {
  try {
    const notificationPermission = await navigator.permissions.query({
      name: 'notifications'
    });

    // In headless mode, this often returns unexpected values
    // or throws errors that wouldn't occur in real browsers

    if (notificationPermission.state === 'denied' &&
        Notification.permission === 'default') {
      flagAsSuspicious();
    }
  } catch (e) {
    // Permission query failures can indicate headless mode
    flagAsSuspicious();
  }
}

4. WebGL Fingerprinting

WebGL rendering reveals GPU information that’s hard to fake.

function getWebGLInfo() {
  const canvas = document.createElement('canvas');
  const gl = canvas.getContext('webgl') || canvas.getContext('experimental-webgl');

  if (!gl) {
    return { suspicious: true, reason: 'No WebGL support' };
  }

  const debugInfo = gl.getExtension('WEBGL_debug_renderer_info');

  if (!debugInfo) {
    return { suspicious: true, reason: 'No debug info extension' };
  }

  const vendor = gl.getParameter(debugInfo.UNMASKED_VENDOR_WEBGL);
  const renderer = gl.getParameter(debugInfo.UNMASKED_RENDERER_WEBGL);

  // Headless browsers often have suspicious renderer strings
  const suspiciousRenderers = [
    'SwiftShader',
    'llvmpipe',
    'Software Rasterizer',
    'Google SwiftShader'
  ];

  if (suspiciousRenderers.some(r => renderer.includes(r))) {
    return { suspicious: true, reason: 'Software renderer detected' };
  }

  return { suspicious: false, vendor, renderer };
}

Why this works: Headless Chrome uses SwiftShader for WebGL rendering. Real browsers use the actual GPU. This is very hard to spoof without a real GPU.

5. Canvas Fingerprinting Anomalies

Canvas rendering produces unique outputs based on hardware and software. Headless browsers produce distinctive patterns:

function getCanvasFingerprint() {
  const canvas = document.createElement('canvas');
  canvas.width = 200;
  canvas.height = 50;
  const ctx = canvas.getContext('2d');

  // Draw text with specific font
  ctx.textBaseline = 'top';
  ctx.font = '14px Arial';
  ctx.fillStyle = '#f60';
  ctx.fillRect(125, 1, 62, 20);
  ctx.fillStyle = '#069';
  ctx.fillText('Cwm fjordbank glyphs vext quiz', 2, 15);
  ctx.fillStyle = 'rgba(102, 204, 0, 0.7)';
  ctx.fillText('Cwm fjordbank glyphs vext quiz', 4, 17);

  // Get data URL
  const dataURL = canvas.toDataURL();

  // Hash the result
  return hashString(dataURL);
}

// Compare against known headless fingerprints
const knownHeadlessFingerprints = [
  'abc123...', // Headless Chrome Linux
  'def456...', // Headless Chrome Windows
  // etc.
];

const fingerprint = getCanvasFingerprint();
if (knownHeadlessFingerprints.includes(fingerprint)) {
  flagAsBot();
}

6. Audio Context Fingerprinting

AudioContext processing produces hardware-dependent outputs:

function getAudioFingerprint() {
  return new Promise((resolve) => {
    const audioContext = new (window.AudioContext || window.webkitAudioContext)();
    const oscillator = audioContext.createOscillator();
    const analyser = audioContext.createAnalyser();
    const gainNode = audioContext.createGain();
    const scriptProcessor = audioContext.createScriptProcessor(4096, 1, 1);

    oscillator.type = 'triangle';
    oscillator.frequency.setValueAtTime(10000, audioContext.currentTime);

    gainNode.gain.setValueAtTime(0, audioContext.currentTime);

    oscillator.connect(analyser);
    analyser.connect(scriptProcessor);
    scriptProcessor.connect(gainNode);
    gainNode.connect(audioContext.destination);

    oscillator.start(0);

    scriptProcessor.onaudioprocess = function(event) {
      const output = event.inputBuffer.getChannelData(0);
      const fingerprint = output.slice(4500, 5000).reduce((a, b) => a + b, 0);

      oscillator.disconnect();
      scriptProcessor.disconnect();
      analyser.disconnect();
      gainNode.disconnect();

      resolve(fingerprint);
    };
  });
}

Detection logic: Headless browsers produce consistent, artificial audio fingerprints. Real browsers vary based on hardware.

7. Timing and Behavioral Analysis

Human behavior has natural variability. Automation is consistent:

class BehaviorAnalyzer {
  constructor() {
    this.events = [];
  }

  trackMouseMove(event) {
    this.events.push({
      type: 'mousemove',
      x: event.clientX,
      y: event.clientY,
      timestamp: Date.now()
    });
  }

  trackClick(event) {
    this.events.push({
      type: 'click',
      x: event.clientX,
      y: event.clientY,
      timestamp: Date.now()
    });
  }

  analyze() {
    // Check for perfectly straight mouse movements
    const moves = this.events.filter(e => e.type === 'mousemove');
    const straightLineScore = this.calculateStraightness(moves);

    // Check for inhuman timing precision
    const timings = moves.map((e, i) =>
      i > 0 ? e.timestamp - moves[i-1].timestamp : 0
    ).slice(1);

    const timingVariance = this.calculateVariance(timings);

    // Bots have very low variance (consistent timing)
    // Humans have high variance (natural pauses, acceleration)

    if (timingVariance < 10) { // Suspiciously consistent
      return { suspicious: true, reason: 'Inhuman timing consistency' };
    }

    if (straightLineScore > 0.95) { // Too straight
      return { suspicious: true, reason: 'Unnatural mouse movement' };
    }

    return { suspicious: false };
  }
}

8. Headless-Specific Object Detection

Some objects only exist in headless mode:

// Check for Playwright-specific objects
if (window.__playwright || window.__pw_manual) {
  flagAsBot();
}

// Check for Puppeteer-specific objects
if (window.__puppeteer_evaluation_script__) {
  flagAsBot();
}

// Check for Selenium-specific objects
if (window.document.$cdc_asdjflasutopfhvcZLmcfl_ ||
    window.document.$chrome_asyncScriptInfo) {
  flagAsBot();
}

// Check for generic automation
if (window.callPhantom || window._phantom) {
  flagAsBot();
}

Note: Stealth plugins remove most of these, but checking is still worthwhile for unsophisticated attackers.

9. Screen and Window Property Analysis

Headless browsers have unusual screen configurations:

function analyzeScreen() {
  const suspicious = [];

  // Check for zero screen dimensions
  if (screen.width === 0 || screen.height === 0) {
    suspicious.push('Zero screen dimensions');
  }

  // Check for mismatched dimensions
  if (window.outerWidth === 0 || window.outerHeight === 0) {
    suspicious.push('Zero outer dimensions');
  }

  // Check for unusual color depth
  if (screen.colorDepth < 24) {
    suspicious.push('Low color depth');
  }

  // Check availWidth vs width (should have taskbar/dock difference)
  if (screen.availWidth === screen.width &&
      screen.availHeight === screen.height) {
    suspicious.push('No taskbar detected');
  }

  // Check for devicePixelRatio
  if (window.devicePixelRatio === 0) {
    suspicious.push('Zero device pixel ratio');
  }

  return suspicious;
}

10. Font Detection

Real browsers have system fonts installed. Headless browsers often have minimal font sets:

function detectFonts() {
  const testFonts = [
    'Arial', 'Verdana', 'Times New Roman', 'Georgia',
    'Comic Sans MS', 'Impact', 'Trebuchet MS',
    'Segoe UI', 'Helvetica Neue', 'Lucida Grande'
  ];

  const baseFonts = ['monospace', 'sans-serif', 'serif'];
  const testString = 'mmmmmmmmmmlli';
  const testSize = '72px';

  const canvas = document.createElement('canvas');
  const ctx = canvas.getContext('2d');

  function getWidth(font) {
    ctx.font = `${testSize} ${font}`;
    return ctx.measureText(testString).width;
  }

  const baseWidths = {};
  baseFonts.forEach(font => {
    baseWidths[font] = getWidth(font);
  });

  const detectedFonts = testFonts.filter(font => {
    return baseFonts.some(baseFont => {
      return getWidth(`${font}, ${baseFont}`) !== baseWidths[baseFont];
    });
  });

  // Headless browsers typically have fewer fonts
  if (detectedFonts.length < 5) {
    return { suspicious: true, fonts: detectedFonts };
  }

  return { suspicious: false, fonts: detectedFonts };
}

Server-Side Detection

Client-side detection can be bypassed. Combine it with server-side analysis.

TLS Fingerprinting

The TLS handshake reveals the true client identity:

Client claims: Chrome 120
TLS fingerprint: Node.js/Puppeteer

Verdict: Spoofed user agent

WebDecoy’s TLS fingerprinting catches this automatically.

HTTP Header Analysis

Headless browsers often have incomplete or inconsistent headers:

def analyze_headers(headers):
    suspicious = []

    # Check for Accept-Language
    if 'accept-language' not in headers:
        suspicious.append('Missing Accept-Language')

    # Check for Sec-CH-UA (Client Hints)
    if headers.get('user-agent', '').includes('Chrome') and \
       'sec-ch-ua' not in headers:
        suspicious.append('Missing Client Hints for Chrome')

    # Check header order (browsers have consistent order)
    expected_order = ['host', 'connection', 'sec-ch-ua', 'user-agent']
    actual_order = list(headers.keys())[:4]
    if actual_order != expected_order:
        suspicious.append('Unusual header order')

    return suspicious

Request Pattern Analysis

Track behavior across the session:

• Asset loading - Real browsers load CSS, JS, images
• Request timing - Humans have natural pauses; bots are consistent
• Navigation patterns - Real users browse; bots target specific pages
• Cookie handling - Session cookies should persist properly

Honeypot Detection for Headless Browsers

The most reliable technique: invisible interactions that only bots trigger.

Hidden Link Honeypots

<a href="/admin-panel-backup"
   style="position:absolute;left:-10000px;top:-10000px;"
   aria-hidden="true">
  Admin Panel
</a>

Headless browsers parsing HTML will find and potentially follow this link. Humans never see it.

Invisible Form Fields

<form action="/submit">
  <input type="text" name="email" />
  <input type="text" name="name" />

  <!-- Honeypot field - hidden from humans -->
  <div style="position:absolute;left:-9999px;">
    <input type="text" name="website" tabindex="-1" autocomplete="off" />
  </div>

  <button type="submit">Submit</button>
</form>

If website is filled, it’s a bot.

Time-Based Honeypots

const formLoadTime = Date.now();

form.addEventListener('submit', (e) => {
  const submitTime = Date.now();
  const elapsed = submitTime - formLoadTime;

  // Humans take at least a few seconds to fill forms
  if (elapsed < 2000) {
    e.preventDefault();
    flagAsBot();
  }
});

Learn more in our endpoint decoys guide.

Implementing Comprehensive Detection

Detection Score Approach

Don’t block on a single signal. Combine multiple indicators:

class HeadlessDetector {
  constructor() {
    this.score = 0;
    this.signals = [];
  }

  addSignal(name, weight, detected) {
    if (detected) {
      this.score += weight;
      this.signals.push(name);
    }
  }

  async analyze() {
    // Navigator checks
    this.addSignal('webdriver', 30, navigator.webdriver === true);
    this.addSignal('plugins_empty', 15, navigator.plugins.length === 0);

    // Chrome object checks
    this.addSignal('chrome_missing', 20, !window.chrome);
    this.addSignal('chrome_runtime_missing', 15,
      window.chrome && !window.chrome.runtime);

    // WebGL checks
    const webgl = getWebGLInfo();
    this.addSignal('software_renderer', 25, webgl.suspicious);

    // Screen checks
    const screenIssues = analyzeScreen();
    this.addSignal('screen_anomalies', 20, screenIssues.length > 0);

    // Font checks
    const fonts = detectFonts();
    this.addSignal('limited_fonts', 15, fonts.suspicious);

    // Automation objects
    this.addSignal('playwright_detected', 50, !!window.__playwright);
    this.addSignal('puppeteer_detected', 50,
      !!window.__puppeteer_evaluation_script__);

    return {
      score: this.score,
      isBot: this.score >= 50,
      signals: this.signals
    };
  }
}

// Usage
const detector = new HeadlessDetector();
const result = await detector.analyze();

if (result.isBot) {
  // Block or challenge
  console.log('Bot detected:', result.signals);
}

Progressive Challenge System

Don’t block immediately. Use progressive challenges:

1. Passive detection - Score based on signals
2. Low-friction challenge - JavaScript puzzle
3. Medium-friction challenge - Invisible CAPTCHA
4. High-friction challenge - Visual CAPTCHA
5. Block - Deny access

This approach catches bots while minimizing false positives for legitimate users.

Staying Ahead of Evasion

The arms race continues. Stealth plugins evolve, and so must detection.

Monitor for New Evasion Techniques

• Follow browser automation communities
• Test your detection against latest stealth plugins
• Monitor security research publications

Combine Multiple Detection Layers

No single technique is foolproof. Combine:

• Client-side fingerprinting
• Server-side TLS analysis
• Behavioral analysis
• Honeypot detection

Use Machine Learning

Train models on known bot vs human sessions:

• Feature extraction from all detection signals
• Continuous model updates with new attack patterns
• Anomaly detection for novel attack techniques

Conclusion

Headless browser detection in 2025 requires sophistication. The old tricks don’t work against Playwright with stealth plugins. You need multiple detection layers working together.

Key takeaways:

1. Single signals fail - Use scoring across multiple indicators
2. Stealth plugins aren’t perfect - WebGL, audio, and behavioral analysis still work
3. Honeypots are reliable - Zero false positives for hidden element interaction
4. Server-side matters - TLS fingerprinting catches spoofed user agents
5. Stay updated - The arms race continues; detection must evolve

WebDecoy provides comprehensive headless browser detection:

• TLS fingerprinting to verify browser identity
• Behavioral analysis to catch automation patterns
• Honeypot decoys for definitive bot detection
• SIEM integration for enterprise visibility

Don’t let headless browsers win. Implement layered detection and stay ahead of the automation arms race.

Need help implementing headless browser detection? Contact our team or explore WebDecoy features.

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