[hk__2]

Which websites?

[wodenokoto]

No, the broader concept of how to dissect the behaviour to figure out the api endpoints called, what was sent to them, what was returned, etc.

[tamimio]

MITM proxy, ZAP, fiddler, and Burp suite are some tools to start with, and wireshark/postman just in case you needed it. Rest is just your knowledge in JavaScript mostly.

[xchkr1337]

I don't think these tools are particularly suitable for reverse engineering websites, it's much easier to use devtools and userscripts