[59nadir]

You don't need a parser library; writing the tokenizer + parsing logic isn't a very time consuming endeavor and the code doesn't suffer from it either. The upside is also that you're not taking on some monstrosity of a library for something you can implement in a tenth of the lines yourself. You'll also end up with something you actually fully understand yourself as well, which should be a big plus.

[laurencerowe]

While I suspect I would learn more writing a tokenizer and parsing logic myself I find grammars much easier to read and maintain.

ANTLR is pretty good and is supported across several languages and something I had previously used for some quick Elasticsearch query syntax munging in Python. It also means you can often start from an already existing grammar.

The JS version of ANTLR didn't seem to work for me so for the SQL/JSONPath stuff ended up using the Moo lever and Nearly parser which was rather pleasant. https://nearley.js.org