British National Corpus

British National Corpus

If you are uncertain about the use of a word or tense, checking it out in the corpus is probably the friendliest way to sort everything out because you get to see how people in the English world use it in a real life context (contrary to all these abstract, elaborated, very often decontextualized and unhelpful notes you'd get in a gramma book).

It's reliable, convenient and last but not least, free.