[0x6c6f6c]

I have usually explained to my teams that you only should be doing this at the boundaries of the system. User input, raw files, request bodies, etc. are places where you would _need_ to determine an actual type for an otherwise unknown value.

Even then, a solid validation/parsing library like Zod is a better choice than casting, it is much less error prone at ensuring you have the right type applied.

Beyond that boundary, casting with `as unknown` is a massive code smell and often introduces any further use of that data to invalid type errors. I'll refer to this as "force casting", because simply casting "x as T" with sufficient strictness configured will still fail type checking if x is not compatible with T, and that can be fine for certain cases like reducing a complex type or giving an inferred parser type a form that fits your domain types.

Developers that force cast too readily can end up creating hundreds or even thousands of type errors in the codebase over time, and they are pretty quickly revealed once you peel away the casting. The same is true when starting from an `any`, where every reference thereon is equivalent to a force cast.

There can be some complex typing scenarios that do require it, but even then a good type guard works better even if certain cases can be semantically equivalent, you can write tests around guards as they're just functions, ensuring some logical correctness to the typing.

The simplest but maybe odd way to judge whether a casting is used the wrong way is to ask "are you lying to the type system?". If so, how can you better portray that type correctly (validation that determines a correct type for you (e g. Zod) or type guards).

[jmull]

Yes, using something like zod at boundaries is the right approach.

(Personally, I'm not convinced zod itself is the way to go -- I'm suspicious of its lack of stability. The last thing I want to do is redevelop the boundaries of my system in a few years because zod 4 has been killed off in favor of zod 5, and then again in a few more years for zod 6, etc.)