Indeed, you might expect that one could pass a “filter” querystring parameter to APIs like GET /recipes/default/tiddlers.json and we may add such support in the future.
However, there’s an interesting alternative approach which uses the new rendered single tiddler endpoint:
The idea is to create a system tiddler that renders the data that you want, and then to request that tiddler as required over HTTP(S).
For example, create a tiddler called $:/MyTiddlers and the following content:
<<jsontiddlers “[tag[HelloThere]]">>
Then request that tiddler via HTTP:
Obviously, this technique requires you to pre-register all of the filters that you need in advance, but it gives you a lot of flexibility as to how the data is represented.
Best wishes
Jeremy