Chinese Grammar Wiki
Chinese Grammar Wiki develops its pages in the same spirit as Wikipedia, and it is probably one of the most comprehensive grammar resources you will find for level A1 to C1 Chinese learners. Furthermore, all of the content is free to be reused as long as it follows their Creative Commons License.
Each article is clearly organized with a table of contents and a sidebar with keywords and references to similar topics. They start with a brief explanation, and then they provide numerous examples of how the grammar would appear in context — these examples dive into the nuances of the language and give you a bigger picture of how to apply the concepts to your everyday life. Depending on your style, this could be less intimidating than, but just as effective as, the in-depth grammar explanations in other resources. You can even use the examples to create Anki flashcards!
Also, for anyone who has struggled with the particle “了”, you will be pleasantly surprised to find 30 articles on Chinese Grammar Wiki, plus links to research, textbooks, and other websites for further reading.
Make sure to bookmark this website for a quick reference during your study sessions!