simple-validators

A TypeScript validation library (v1.2.0, actively maintained) for building explicit, customizable schema validators. Unlike libraries like zod or yup, it does not infer schemas from types or use method chaining; instead it provides composable validation functions (validateString, validateBoolean, validateEmail, validateObjectKeys, etc.) that return undefined on failure and collect error/warning messages via options. It is part of the MyST Markdown ecosystem, updated regularly alongside mystmd releases. Key differentiator: no magic, full control over error reporting with user-supplied log functions, and explicit handling of required vs optional keys.