> unless the language compiler/interpreter uses tree-sitter for parsing Doubtful, last time I tried tree-sitter would parse invalid inputs without even tagging

> unless the language compiler/interpreter uses tree-sitter for parsing Doubtful, last time I tried tree-sitter would parse invalid inputs without even tagging any errors in the parse tree. For example, it would silently accept extra tokens, or keywords in the place of identifiers. Replacing the built-in lexer and then validating the parse tree for correctness would be close to writing the grammar twice. And accepting partially correct inputs within the compiler toolchain isn't too hard, so I don't really see the advantage of agreeing on tree-sitter and not just on a parse tree representation that editors can then query, as you then suggested. If the big deal is having it execute client-side or being sandboxed, I feel that's orthogonal to parsing algorithms.