Ajv

Ajv is a JSON Schema validator for JavaScript. It checks that data matches a schema before your code uses it.

Ajv takes a schema that describes the shape of your data and checks incoming values against it. It compiles each schema into optimized JavaScript, so checks run quickly. You describe rules declaratively instead of writing a custom check for every field. When data fails, Ajv returns a list of errors that explains what went wrong.

• Compiles schemas into optimized JavaScript
• Supports JSON Schema drafts 04 through 2020-12
• Supports JSON Type Definition (RFC 8927)
• Works in Node.js, browsers and Electron apps
• Returns error details when data is invalid

Ajv suits backend engineers who validate API payloads, frontend developers who check form or config data, and library authors who need a dependable schema check. Teams that already write JSON Schema files will find it a direct fit.

Ajv is open source under the MIT license, so it is free to use. It runs in Node.js, in browsers and in Electron apps. Because it follows the JSON Schema standard, the rules are only as good as the schema you write, so schema design still needs care.