need RAM & SWAP Memory monitoring Threshold

I wish to setup monitoring alerts upon used memory percentage. I had setup 0-80% used RAM as Green (good) 81-90% as yellow(acceptable) 91-95% as orange(warning) 96+ as Red(critical) However, i see that my current usage of RAM is 99% yet everything seems working smoothly and that makes everyone feel 96+ as Red(critical) is not the right criteria to Alert for critical. I noticed that despite 99% usage of RAM the swap memory was 100% free. $ free -m total used free shared buff/cache available Mem: 15883 1672 273 57 13938 13766 Swap: 2047 0 2047 Thus, my query is should I also check for swap memory or only the swap memory to send out Alerts and what would that appropriate threshold be for RAM as well as swap memories ?