Chrome Incognito Extensions: A Developer’s Guide

Chrome’s incognito mode provides a privacy-focused browsing session that does not save history, cookies, or site data. However, many users expect their extensions to work smoothly in this mode—and developers need to understand how to handle incognito-specific behavior properly.

This guide covers the technical details of Chrome incognito extensions, including configuration options, API limitations, and implementation patterns that developers and power users should know.

How Incognito Mode Affects Extensions

When a user opens an incognito window, Chrome applies specific rules to extensions by default:

1. Extensions are disabled unless explicitly allowed
2. Separate storage is used for extension data
3. Background pages may behave differently depending on manifest version
4. Some APIs have reduced functionality or require special permissions

The default behavior blocks extensions from reading or modifying incognito sessions. Users must manually grant permission for each extension they want to use in incognito mode.

Configuring Extension Manifest

To support incognito mode, your extension must declare the incognito permission in the manifest. Here is an example for Manifest V3:

{
  "manifest_version": 3,
  "name": "My Privacy Extension",
  "version": "1.0",
  "permissions": [
    "storage",
    "activeTab",
    "scripting"
  ],
  "incognito": "spanning"
}

The incognito field accepts three values:

• spanning (default): The extension runs in both regular and incognito windows, but uses separate storage
• split: The extension uses different background scripts for incognito and regular windows
• Not specified: The extension does not work in incognito mode

For most extensions, spanning is the appropriate choice. Use split when you need distinct behavior for incognito sessions.

Detecting Incognito Mode in Your Extension

Your extension code can detect whether it is running in an incognito window using the chrome.runtime.lastError pattern or by checking the tab’s incognito status:

chrome.tabs.query({ active: true, currentWindow: true }, (tabs) => {
  if (chrome.runtime.lastError) {
    console.error(chrome.runtime.lastError);
    return;
  }
  
  const currentTab = tabs[0];
  if (currentTab.incognito) {
    console.log("Running in incognito mode");
    // Adjust behavior accordingly
  }
});

Alternatively, you can use the chrome.extension.isAllowedIncognitoAccess API to check whether the user has granted incognito permission to your extension:

chrome.extension.isAllowedIncognitoAccess((isAllowed) => {
  if (isAllowed) {
    console.log("Incognito access is enabled");
  } else {
    console.log("Incognito access is disabled - prompt user to enable");
  }
});

Storage Behavior in Incognito Mode

Extensions using chrome.storage behave differently in incognito mode. With the spanning behavior (default), your extension gets separate storage for incognito sessions:

• chrome.storage.local - Uses separate local storage in incognito
• chrome.storage.sync - Data does not sync across regular and incognito profiles
• chrome.storage.session - Data is cleared when the incognito window closes

If you need to share data between regular and incognito sessions, you must explicitly handle this with your own sync mechanism or warn users that data will be isolated.

Background Service Workers and Incognito

Manifest V3 uses service workers as background scripts. In incognito mode with spanning behavior, the same service worker handles both regular and incognito tabs. You need to check the context when handling events:

chrome.runtime.onMessage.addListener((message, sender, sendResponse) => {
  if (sender.tab && sender.tab.incognito) {
    // Handle incognito-specific logic
    handleIncognitoMessage(message, sender, sendResponse);
  } else {
    // Handle regular browsing logic
    handleRegularMessage(message, sender, sendResponse);
  }
  return true; // Keep message channel open for async response
});

With split behavior, Chrome creates a separate background context for incognito mode, which runs its own instance of your background script.

Practical Implementation Patterns

Pattern 1: Warn Users About Incognito

function checkIncognitoAndWarn() {
  chrome.tabs.query({ active: true, currentWindow: true }, (tabs) => {
    if (tabs[0]?.incognito) {
      chrome.tabs.sendMessage(tabs[0].id, {
        type: "INCognito_WARNING",
        message: "Some features may be limited in incognito mode."
      });
    }
  });
}

Pattern 2: Disable Specific Features

function getFeatureFlags(incognito) {
  return {
    analytics: !incognito,    // Disable analytics in incognito
    syncData: !incognito,     // Disable sync in incognito
    persistentStorage: !incognito, // Use session storage
    backgroundFetch: !incognito   // Disable background operations
  };
}

Pattern 3: Clear Sensitive Data on Incognito Exit

chrome.tabs.onRemoved.addListener((tabId, removeInfo) => {
  if (removeInfo.isWindowClosing) {
    chrome.tabs.query({ currentWindow: true }, (tabs) => {
      const hasIncognitoTab = tabs.some(tab => tab.incognito);
      if (!hasIncognitoTab) {
        // Clear all incognito-related data when incognito window closes
        chrome.storage.session.clear();
      }
    });
  }
});

User Experience Considerations

When designing extensions that work with incognito mode, consider these user experience factors:

Permission Requests: Users see a specific prompt when they first install an extension that supports incognito. Make sure your extension’s purpose is clear so users feel comfortable granting access.

Visual Indicators: Consider adding a visual indicator in your extension popup when running in incognito mode so users understand why certain features might behave differently.

Documentation: Clearly document which features work in incognito mode and which do not. Users deserve transparency about privacy-related behavior.

Common Pitfalls to Avoid

1. Assuming persistent storage: Data in chrome.storage.session is cleared when incognito windows close
2. Ignoring split mode: If using split behavior, remember you have two separate extension contexts
3. Missing error handling: Always check chrome.runtime.lastError in callback-based APIs
4. Blocking incognito entirely: Unless there’s a valid security reason, blocking incognito creates a poor user experience

Conclusion

Chrome incognito extensions require thoughtful implementation to provide good user experience while respecting privacy expectations. By properly configuring your manifest, handling storage appropriately, and detecting incognito context in your code, you can build extensions that work smoothly in both regular and private browsing sessions.

Understanding these nuances helps developers create more robust extensions and empowers power users to make informed decisions about their privacy tools.

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• Claude Code for Beginners: Complete Getting Started Guide
• Best Claude Skills for Developers in 2026
• Claude Skills Guides Hub

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