I support HTML, JS, Python and CSS. For HTML, (not technically an AST), I give the LLM the original-file HTML source, and then I instruct it to write python code that uses BeautifulSoup to modify the HTML. Then I get the string back from python of the full HTML file, modified according to the user prompt.

For python changes I use ast and astor packages, for JS I use esprima/escodegen/estraverse, and for CSS I use postcss. The process is the same for each one: I give the original input souce file, and I instruct the LLM to parse the file into AST form and then write code that modifies that AST.

I blogged about it here if you want more details! https://codeplusequalsai.com/static/blog/prompting_llms_to_m...