We use it heavily for backend code, and it is a bit of a hot path for our use cases. However the biggest issue is how big the types are by default. I had a 500 line schema file that compiled into a 800,000 line .d.ts file — occupying a huge proportion of our overall typechecking time.

Yup, maintained an e-commerce site where the products were coming from a third party api and the products often had 200+ properties and we often needed certain combinations of them to be present to display them. We created schemas for all of them and also had to transform the data quite a bit and used union types extensively, so when displaying a product list with hundreds of these products, Zod would take some time(400+ ms) for parsing through that. Valibot took about 50ms. And the editor performance was also noticeably worse with Zod, taking up to three seconds for code completion suggestions to pop up or type inference to complete - but truth be told valibot was not significantly better here at the time.

I agree though, that filling your website with tracking crap is a stupid idea as well.

Zod is the default validator for https://github.com/gajus/slonik.

Zod alone accounts for a significant portion of the CPU time.

I’ve used it on the backend to validate and clean up tens of thousands of documents from Elasticsearch queries, and the time spent in Zod was very much noticeable

My issue is ts server perromance not so much runtime