Looking up the Nitty-Gritty:
Here are some of my favorite online resources for quick reminders on grammar, general rules of composition, and the meanings and spellings of words.
OWL Purdue University's vast collection of free online writing resources. For general writing mechanics (including grammar and punctuation), this is a good place to start: https://owl.english.purdue.edu/owl/section/1/.
The site also has links to MLA and APA style guides.
Etymological Dictionary Learning the origins of words and their changing meanings over time can often add surprising depth to your writing and thinking.
Linguee Working with a foreign-language source text and unsure about the meaning of a particular word? This site provides translations of words in different contexts. It's no good as a dictionary if you don't already know a language, but if you are hunting for just the right word to complete a translation, it's pure gold.
The Oatmeal. Grammar is a funny thing indeed.