Use Majestic, Moz and AHrefs tools.
Real way to detect bad backlinks is to manually vet each one and decide whether it looks natural or not. If you’re unsure, here are some other ways of deciphering a harmful backlink:
Low domain authority (and low Trust Flow if you’re using Majestic)
Links from domains in countries where your business has no target audience
Links from websites with no relevance to your business or content
A high volume of links coming from a single source
Over-optimised, keyword-stuffed anchor text
Links from domains with very low social shares
Comment or forum spam