> Is it more efficient resource and time-wise to rewrite everything in [Language of choice], or to comb through the currently existing code manually and with sp

> Is it more efficient resource and time-wise to rewrite everything in [Language of choice], or to comb through the currently existing code manually and with special tools to find bugs and fix them? One thing you're missing is that "comb[ing] through the currently existing code manually" doesn't help you in the future. Unless you have an absolute code freeze new code keeps getting written which can (depending on the language) affect the correctness of distant already reviewed code. So even if you can absolutely ensure that the code as it exists today is perfect (which is already an exceedingly thing to do), you need to keep that effort up continuously, lest a code change causes prior invariants to no longer be met.