json-gate

A friendly, fast JSON schema validator for JavaScript, supporting JSON Schema Draft 3. Current stable version is 0.8.23. The library is minimal and synchronous or asynchronous. It produces detailed, human-friendly error messages. Unlike many modern validators, it only supports Draft 3 (not Draft 4+ or 2020-12), making it a legacy choice. The API is simple: create a schema and validate objects. It is not actively maintained, as the last release was years ago. It has no dependencies.