Hello @vn168it and @danielhong,
Thank you for contacting Rank Math support and bringing your concern to our attention.
Our headless CMS does return a JSON format response as you can see in my screenshot here, however, the content of the “head” key currently contains the HTML format as these data were intended to be inserted for the head tag. Using this format will also make it easy to apply to the frontend as you don’t have to parse the data.
With that said, we currently don’t have any plans on changing the response format.
Hope that helps.
Thank you.