If you've ever stored JSON locally and had the schema change over time, you know the pain of trying to keep it up-to-date as your application changes. You end up with defensive checks everywhere, or data that silently breaks when the shape changes underneath you.

I've faced this problem a few times lately, so I built json-up to handle this with a migration chain. Define versioned steps with Zod schemas, and the library walks your data forward from whatever version it's at, validating at each step with full TypeScript inference.

Zero runtime deps, works with Zod v3 and v4, and three distinct error types for precise failure handling.

Have a poke around!