Norwegian grammar checker
I wanted to share this useful link I found: http://regdili.hf.ntnu.no:8081/studentAce/parse
You can type in a Norwegian sentence and it will tell you if there are any grammatical mistakes. If you make a mistake it will tell you what kind of mistake it is, and it will provide a link with an explanation of the grammar.
THIS IS NOT A RELIABLE SENTENCE CHECKER
I know this is an old post, but since people like me are still finding it I thought I'd leave a comment. Sure it may work for very simple sentences but it also gives a lot of false positives. I was messing with word order and was told the following sentence was correct:
"Hver dag lager sammen vi mat."
This surprised me and so I asked a native who then told me it was blatantly incorrect.
Unfortunately, there is no magic sentence checker online and if you are unsure if what you are writing is correct or not you should ask an expert. If you don't know any native speakers like me you can usually find someone on the Norwegian language learning subreddit: https://www.reddit.com/r/norsk/
Fysisk aktivitet. Fysisk aktivitet er veldig viktig i livet mitt. Jeg tror vi går minst 30 minutter hver dag. Hvis du er fysisk aktiv, kan du tilbringe et sunt liv. fysisk aktivitet er viktig for å unngå sykdommer som høyt blodsukker, hjerneslags,hjerteinfarkt og andre sykdommer.
I found one that works and even addresses what your grammar issues are. It's coupled with an article that will teach you some good essentials of grammar
The checker: http://regdili.hf.ntnu.no:8081/studentAce/parse