Using mitmproxy to intercept your packets is a convenient way to inspect a browser's network traffic.

It's pretty straightforward to setup on a desktop computer:

  1. Install mitmproxy (apt install mitmproxy on Debian) and start it:

     mitmproxy --mode socks5 --listen-port 9000

  2. Start your browser specifying the proxy to use:

     chrome --proxy-server="socks5://localhost:9000"
 brave-browser --proxy-server="socks5://localhost:9000"

  3. Add its certificate authority to your browser.

At this point, all of the traffic from that browser should be flowing through your mitmproxy instance.

Android setup

On Android, it's a little less straightforward:

  1. Start mitmproxy on your desktop:

     mitmproxy --mode regular --listen-port 9000

  2. Open that port on your desktop firewall if needed.

  3. On your Android device, change your WiFi settings for the current access point:
  4. Proxy: Manual
  5. Proxy hostname: 192.168.1.100 (IP address of your desktop)
  6. Proxy port: 9000
  7. Turn off any VPN.
  8. Turn off WiFi.
  9. Turn WiFi back on.
  10. Open http://mitm.it in a browser to download the certificate authority file.
  11. Open the system Settings, Security and privacy, More security and privacy, Encryption & credentials, Install a certificate and finally choose CA certificate.
  12. Tap Install anyway to dismiss the warning and select the file you just downloaded.

Once you have gone through all of these steps, you should be able to monitor (on your desktop) the HTTP and HTTPS requests made inside of your Android browsers.

Note that many applications will start failing due to certificate pinning.