tosijs-schema: A Schema-First Validation Library Using JSON Schema as Source of Truth

Summary

tosijs-schema is a schema-first validation library that positions JSON Schema as the source of truth for data validation, contrasting with Zod's approach of deriving validation from TypeScript types. The library enables developers to define schemas once and derive both TypeScript types and validation logic from them, making it particularly useful for data that crosses boundaries like APIs, LLMs, databases, or documentation. The article explains the library's philosophy, compares it to Zod, and provides implementation details and usage examples.