Everyone thinks about safety before visiting a certain country and city. That is completely normal and absolutely expected nowadays.
Travelling is amazing and awesome experience, so why ruin it by not checking out which is is safe for visiting and sightseeing.
Dusseldorf is almost 100% safe city.
You can walk, run, shop and visit as much as you like and be absolutely safe. People are kind and will help you with directions whether you speak German or not.
With so many amazing places and tourist attractions to see, you can spend your time without a worry about Dusseldorf safety, because during the day it’s absolutely charming, vibrating city.
In the evening, especially during holidays, there are huge crowds of people, but there are guards everywhere, so you don’t have to worry.
Potential worrying situations are during weekends when there are football games. Then, specially on main train station, it’s absolutely too crowded and loud. So, if you aren’t a fan of noise, pushing and crowds, just avoid that. There is a hightened security detail during that time, but still it can be dangerous. Possible mugging or just accidental pushing.
Similar is with some big events, such as Rheinkirmes but again, security is tight and does great job together with numerous young people who give directions and keep order. Though, if you want to take a train or tram, prepare yourself to barely take a proper breath, let alone stand normally or sit.
But, experience, fun and great time is definitely worth the trouble.
Bottom line is, Dusseldorf is a safe city where you can feel comfortable and pleasant.