No matter how well you learned grammar and punctuation, there will be times when you need to check whether something is correct or not. Whether it’s a case of not remembering for sure, being told your way is wrong, or simply not knowing, having somewhere to check is invaluable. The only problem is that if you don’t know for certain, how do you know if the resource is right or not?
While you can buy the newest MLA handbook or grammar guide from a big name that’s probably accurate, when it comes to a reliable grammar resource, I recommend the Purdue Online Writing Lab (OWL).
This online resource discusses word usage, punctuation, and citation (APA, MLA, and Chicago styles). It is very good about providing examples, and it gives in-depth rules for most of the punctuation and grammar problems you’re likely to encounter. The link I’ve provided is to the grammar section, but if you look at the site map, you’ll see that there is much more, including articles written specifically for people learning English as a second language (ESL). There are even sections about writing for different university levels, different careers, and job applications.
When it comes to reliable resources, OWL is truly a comprehensive guide to writing rules for American English. Even better: it’s free!