Ajv

Ajv, short for Another JSON Schema Validator, is a fast, battle-tested JSON Schema validator for JavaScript. It runs in Node.js and in web browsers and is widely used to validate data against JSON Schema definitions.

Ajv compiles schemas into efficient JavaScript functions, enabling high validation throughput. It supports a broad range of JSON Schema drafts through a plugin architecture and provides features such as custom keywords, formats, asynchronous validation, and detailed error reporting. It accepts references to other schemas, enabling modular schema composition, and offers strict mode to catch common mistakes.

Users typically create an Ajv instance, compile a schema, and reuse the compiled function for multiple data objects. The library emphasizes performance through caching and incremental compilation, and can report validation errors with path and keyword details.

Ajv is maintained as an open source project with an extensive ecosystem, including companion packages for formats and CLI usage, and integrations with build tools and frameworks. It is distributed under the MIT license and is one of the most popular JSON Schema validators in the JavaScript community.

See also JSON Schema, Node.js, npm.