They can oneshot relatively simple parsers/encoders/decoders with a proper spec, but it’s a completely different ballgame when you’re trying to parse a very domain knowledge heavy file format (like the format electronics CAD) with decades of backwards compatible cruft spread among hundreds of megabytes of decompiled Delphi and C# dlls (millions of lines).

The low level parts (OLE container, streams and blocks) are easy but the domain specific stuff like deserializing to typed structs is much harder.