If it's anything like the Swedish model, it's not as easy as that. You can of course solicit someones tax return from the Tax Agency (as it's a public record) and read how much income they declared, but it's not as easy as typing in someone's name into an API and getting "They make X per month".
The process is quite easy and can be done online [1] but since 2014, the person in question will be informed via email about the request. But as anyone can request salaries, you can just ask someone else to request your neighbour's salary if you don't want him to see it was you. Journalists are exempt from that and can see any tax report without notification.
There is no e-mail being sent, but I think many people actually believe that the person they search is notified - would explain why so few people have used it in recent years.
Everyone who has searched for your name is listed in a sub-section / "tab", listed as a link on the same page where you can search for the information of others. I imagine that very few people are looking at that, especially not a few days after the initial "OMG now you can look up what everybody makes" articles in the newspapers.