If start out in the middle with BNF grammar, can get drag/drop diagram/grammar highlighter for use in codemirror[0] or mess around with BNF linting [1][2][3][4].

[0] https://bnfc.digitalgrammars.com/

[1] : https://dl.acm.org/doi/10.1145/3278186.3278193

[2] : https://www.researchgate.net/figure/Overview-of-Grammarinato...

[3] bullwinkle : https://github.com/sylvainhalle/Bullwinkle

[4] : https://news.ycombinator.com/item?id=30822544