If you’re developing a Chrome extension using Manifest V3 and loading it with --load-extension, you might run into a frustrating issue: your service worker code gets cached and refuses to update, even when you’ve changed the code and bumped the version number.

A Stack Overflow user asked a question about this many years ago but never received a proper answer.

The Problem

Manifest V3 introduced service workers as the replacement for persistent background pages. While this is generally a good architectural change in terms of resource requirements, Chrome’s caching behavior for service workers is extremely aggressive. Even when you update your extension code, bump the version in manifest.json, and restart the browser, the old service worker code may still be running!

This happens because Chrome caches the compiled service worker script separately from the extension files themselves. The cache can persist across browser restarts and extension reloads.

How to Verify You Have Stale Cache

If you suspect your service worker is cached, check the Chrome profile. Look in the Preferences file specifically – this is a JSON file that you first need to pipe through jq to get a proper format:

cat Default/Preferences | jq .extensions.settings.YOUR_EXTENSION_ID.service_worker_registration_info

Replace YOUR_EXTENSION_ID with your actual extension ID (you can find this on the chrome://extensions page when Developer mode is enabled). This prints:

{
  "version": "1.28.1"  // This might be older than your actual extension version!
}

The Solution

The most reliable way to force Chrome to reload your service worker is to manually reload the extension from the Extensions page:

  1. Navigate to chrome://extensions
  2. Enable Developer mode (toggle in the top-right corner)
  3. Find your extension in the list
  4. Click the Reload button (circular arrow icon)

This forces Chrome to re-register the service worker and clear the cached script.

If you’re running Chrome headlessly or in an automated environment, you will need to programmatically reload the extension using Selenium/WebDriver.

Alternatively, you can use a completely new profile directory for testing, which ensures no cached service worker scripts are present. But this will not work if you need persistent data across sessions.

Note: You might be tempted to just delete the Service Worker/ScriptCache directory to force a clean slate. Don’t do this. This directory contains cached scripts for Chrome’s built-in components as well, and deleting it can break Chrome’s internal functionality. Only the extension reload method described above is safe.