Not sure what you mean. There is no hard and fast top down enforced rules. Aside from natural Hack bias at FB, you can use any language you want. People develop

Not sure what you mean. There is no hard and fast top down enforced rules. Aside from natural Hack bias at FB, you can use any language you want. People develop tools in Rust, D, C++, bash, etc. As far as libraries go, there is a mandate to use in-house patched versions of various sdks and libraries, for security/customization reasons. Otherwise, go nuts. People write a whole lot of in-house software at FB, some of which is later open sourced. > That just doesn't happen at Amazon Oh please. We had a mandate to use Apollo. PHP is banned at Amazon (whatever your view of PHP is, that is a top down directive). The only freedom we actually had at Amazon was to use whatever open source software we could without contributing back to it (I'm sure there are examples where we did, ut not at the scale of FB). And lastly, Amazon was all about telling me what to do. One day I got a phone call and I got moved from front-end app development to backend c++. Nobody asked me if I wanted to do it or if I would be any good at it. FB spends months in bootcamp with teams trying to convince you to join them.