It’s been a while – two-and-a-half years – since I mentioned the useful site canoo.net – free online German language resources / Deutsche Grammatik, Online Wörterbuch zur Rechtschreibung, Flexion und Wortbild(ung?).
I have used it sometimes, but I don’t usually check my German grammar.
The site has now incorporated the latest spelling reform in its dictionaries and grammar pages. It says:
With 250,000 entries generating more than 3 million inflected word forms, Canoo.net is the most comprehensive spelling dictionary and German grammar resource available on the net.
There’s a good site search too.