I think this question may be underspecified. Do you mean web APIs, like their URL structures and request and response objects? Or more like library APIs? I'd ha

I think this question may be underspecified. Do you mean web APIs, like their URL structures and request and response objects? Or more like library APIs? I'd have different standards of beauty for them. One that has always impressed me is the Clang AST matchers API, which allows you to declaratively define a search pattern. You can easily bind a name to any sub-pattern to access this part of the match easily. https://clang.llvm.org/docs/LibASTMatchersReference.html https://clang.llvm.org/docs/LibASTMatchersReference.html