[dozzie]

Depends on what does it need to do, but you most probably will need a regular RPC instead of trivial CRUD (REST) or mostly data query (GraphQL). Though RPC is not fancy nor sexy, so most web developers this days won't even look at that.

[_isus]

The question is intentionally generic as I am trying to find out what most folks would do if they were starting with something fresh. Your comment reminded me I needed to narrow the focus a bit. I edited the question to add an assumption that this is a Web API.

[dozzie]

I don't know why did you get the impression that my comment somehow doesn't apply to API-first web services.

[_isus]

I didn't - it just reminded me that some might take it in a more general way than I intended. :)