I haven’t found any specific research, but I suspect it’s actually the opposite, particularly for models like Claude, which seem to have been specifically train

I haven’t found any specific research, but I suspect it’s actually the opposite, particularly for models like Claude, which seem to have been specifically trained on XML-like structures. My hunch is that the fact that HTML has explicit matching closing tags makes it a bit easier for an LLM to understand structure, whereas markdown tends to lean heavily on line breaks. That works great when you’re viewing the text as a two dimensional field of pixels, but that’s not how LLMs see the world. But I think the difference is fairly marginal, and my hunch should be taken with a grain of salt. From experience, all I can say is that I’ve seen stripped down HTML work fine, and I’ve seen markdown work fine. The one place where markdown clearly shines is that it tends to use fewer tokens.