I like writing parsers, and nowadays just use handwritten recursive descent functions, using a couple of simple utility functions. It is easy to reason about and flexible. I do start each parsing function with a comment stating the informal grammar the function should parse (and LLM autocomplete usually types the rest of the function).

With regard to portability: I've found cross-language parser generators especially unpleasant to work with. Instead, I just implement the parser in a language that runs on all platforms I care about.