Htmx actually can be used with these restrictions, there is an extension to do client side rendering from a JSON response [1]. And you can make htmx send JSON requests instead of form data [2].

The idea is easily extendable to any template engine, so you can keep your device response minimal while enjoying the simplicity of htmx. I will admit though, this approach gets funky much faster, than returning HTML fragments, so you probably shouldn't exclusively build your app with this client-side-templates

[1]: https://htmx.org/extensions/client-side-templates/ [2]: https://htmx.org/extensions/json-enc/