ProperHeaderGuides
Practical, step-by-step fixes for the jobs a header extension is for. Each guide says which steps are free and which need Pro.
How to fix CORS errors on localhost in Chrome
Fix 'blocked by CORS policy' errors while developing on localhost by adding Access-Control-Allow-* response headers in Chrome. Step-by-step, including credentials and preflight requests.
How to add or change request headers in Chrome
Send an Authorization Bearer token, API key, feature flag or any custom HTTP header from Chrome. Step-by-step guide to setting, appending and removing request headers, free.
How to test your local JavaScript on the live site
Redirect a production script to your localhost dev build, or replace a JS, CSS or JSON file's contents in Chrome. A Resource Override replacement for Manifest V3.
How to remove a Content-Security-Policy in Chrome for testing
Strip or rewrite the Content-Security-Policy header in Chrome to test scripts, overrides and debugging tools on sites with a strict CSP. Safely, on just the sites you choose.
How to change the User-Agent header in Chrome
Send a mobile, bot or custom User-Agent header from Chrome on the sites you choose. Free, with one click, and with a clear explanation of what it does and doesn't change.
How to move your ModHeader profiles to ProperHeader
Export your profiles from ModHeader and import them into ProperHeader: headers, URL filters, resource types and redirects convert automatically. What converts, what doesn't, and what to do if ModHeader is already gone.
Switching from ModHeader
ModHeader was removed from Chrome. Here's what happened and what to do.
Google removed ModHeader from the Chrome Web Store in July 2026 after researchers found hidden browsing-data collection code. What was found, whether you're affected, and how to move your header profiles safely.
The ModHeader alternative you don't have to second-guess
Looking for a ModHeader replacement after it was removed from the Chrome Web Store? Compare ProperHeader with ModHeader and Requestly on privacy, features and price, and import your ModHeader profiles in one step.