[roguecoder]

"Need"? Probably not. But unlike microservices they don't really have downsides (at least not with modern IDEs and the automatic refactorings they support) and they do offer some benefits.

Statically-types languages are a form of automatically-verified documentation, and an opportunity to name semantic properties different modules have in common. Both of those are great, but it is awkward that it is usually treated as an all-or-nothing matter.

Almost no language offers what I actually want: duck typing plus the ability to specify named interfaces for function inputs. Probably the closest I've found is Ruby with a linter to enforce RDoc comments on any public methods.

[frollogaston]

I'm fine with types in shared libs, just not in the app layer code, where the cost outweighs the benefit. I think you can do the in-between you describe with Typescript, but every time I've been on a team that says "oh you can use `any`," one day they disallow it. Especially in a big corp where someone turns it into a metric and a promo target.