Check Bandwidth and Add Limitations - Mikrotik Script
This script checks if download on interface is more than 512kbps, if true then queue is added to limit speed to 256kbps.

:foreach i in=[/interface find] do={
    /interface monitor-traffic $i once do={
        :if ($"received-bits-per-second" > 0 ) do={
            :local tmpIP [/ip address get [/ip address find interface=$i] address] ;
            #:log warning $tmpIP ;
            :for j from=( [:len $tmpIP] - 1) to=0 do={
                :if ( [:pick $tmpIP $j] = "/") do={
                    /queue simple add name=$i max-limit=256000/256000 dst-address=[:pick $tmpIP 0 $j] ;
                } 
            }
        }
    }
}