It gives you a rough estimate of income, but should not really be trusted if your goal is to negotiate your salary because you've been checking out your co-workers income.

The salary shown in our skattelisten (tax list) is what's called the general income. That is: All taxable income, minus deductions. This means that the income you see in our tax list is going to be lower, than what it is in reality.

It could also appear much higher, if you've sold something which counts as taxable income, done consulting/side gigs, etc.