Recently did the onsite loop for Meta and noticed there are a ton of great resources for coding questions asked so I won't speak on this since there is nothing new I can add. I got lucky and all 4 questions I was asked I have seen before and did very well here (I am at 400+ questions over 3 years because I know someone will ask). But I did notice there is not many posts about System design. So the way I prepped was doing questions like Design twitter, Design facebook live comments, design a distributed cache. The common ones you expect. Now when I did my System design round I got a quetions I was not expecting and completely unprepared for. My interviewer asked me to design a system that could hack a website (FB messenger) and scan pages / messages without being detected. I had to have alot of hints for the interviewer as to what he was looking for. For this question be prepared to be asked about authentication types, pros cons of different ones, how to spoof them, he also wanted me to dive into how encryption and hashing worked and how I would tackel his problem, and the entire time It was very clear that remaining undetected was important so if you get this question be prepared to speak on that. It seemed he was also looking for a system that was on phones only and the software on the phones can communicate (I think this is impotant for somehow getting the encryption but I'm not sure) he told me to assume there were 10k devices, you cannot install or have access to anything on there servers. When I first started the interview I tried to write down non functional and functional requirments but he told me to go straight into the system as this wasnt important. So be prepared for the flow of the interview to stray from that path if you are used to it. This round went so bad for me since it was not a question I preped for I dont think I got a working system. My recuriter let me know I was rejected and I was able to set up a call with her and even though it is against policy for them to give you feedback I was able to pressure her and she told me I did perfect on the coding questions but my design round was too weak. So take aways from this. System design round is just as imporant as coding. Be prepared to talk about hacking, authentication, spoofing, encryption / hashing and remaining undetected. Also seems for these rounds talking about all these things is not enough you need to at a minimum have some working system. Good luck out there hope this with your system design prep.