The word 'hardly' is correct and usable in written English. You can use it to mean that something is only done or true in a small amount or not at all. For example: "I hardly ever go to the movies.".
This is hardly surprising.
This was hardly surprising.
It hardly matters.
Likewise, our old playroom – the kids are grown up now and hardly anyone goes in there.
Well, hardly.
The two men could hardly be more different.
With a few exceptions, it was hardly possible to imagine Embassy officials or troops in Baghdad taking great risks to get their Iraqi contacts out before we left.
Being a terminologist, I care about word choice. Ludwig simply helps me pick the best words for any translation. Five stars!
Maria Pia Montoro
Terminologist and Q/A Analyst @ Translation Centre for the Bodies of the European Union