Truecaller is an app developed by a Swedish software company which provides an integrated caller id service those who use it.
It runs in Android, BlackBerry OS, iOS, Windows phone, etc.
This is a global telephone directory which uses crowd sourced data to be updated. When you download and install this app on your phone, you are giving it the permission to scan your phone and retrieve the phone numbers saved.
You can use it if you have no problem with your number being on a Swedish Server. You can unlist your number from this service if you want.I value my own privacy as well as others. I don’t use Truecaller and encourage you not to use it.