This repository contains a little web tool that encrypts data with AES-GCM and decrypts the ciphertext with AES-CTR, both via the browser crypto API. This is not intended for any practical use. I created it to better understand the relationship between GCM and CTR.
The tool is deployed to GitHub pages. You can access it here: https://moritzhoeppner.github.io/gcm-vs-ctr/
If you don't understand how this works, check out this little blog post, which describes the idea.