ajv - Efficient JSON Schema Validation for Node.js and Browser

Ajv JSON Schema Validator

Introduction

Ajv is recognized as the fastest JSON schema validator available for both Node.js and browsers. It offers comprehensive support for JSON Schema drafts 04, 06, 07, 2019-09, and 2020-12, and also supports JSON Type Definition as outlined in RFC8927.

Performance

Ajv is designed to be extremely efficient, generating code to convert JSON schemas into super-fast validation functions. It is benchmarked as the fastest JSON validator across multiple comparisons, consistently outperforming other validators in performance tests.

Features

Ajv is packed with features that make it not only fast but also versatile:

Standards Compliance: Implements JSON Schema standards fully, including all validation keywords and OpenAPI extensions.
Remote References: Offers full support for remote references by allowing schemas to be added or compiled for use.
String Handling: Accurately measures string lengths even when involving Unicode pairs.
Validation Modes: Supports "all errors" validation mode to report all errors found rather than stopping at the first error.
Error Messaging: Provides parameterized error messages for easy error identification and resolution.
Internationalization: Error messages can be localized using the ajv-i18n package.
Data Transformation: Can remove additional properties, assign default values, and coerce data types according to schema specifications.
User-Defined Keywords: Supports extensions through ajv-keywords and allows for custom keyword definitions.
Asynchronous Validation: Enables async validation of both user-defined formats and keywords.

Getting Started

Ajv can be easily integrated into projects with a simple installation command:

npm install ajv

It can be used in JavaScript through ESM/TypeScript imports or traditional Node.js require statements. Here is a basic example of its usage:

import Ajv from "ajv"; // or const Ajv = require("ajv");

const ajv = new Ajv();
const schema = {
  type: "object",
  properties: {
    foo: { type: "integer" },
    bar: { type: "string" },
  },
  required: ["foo"],
  additionalProperties: false,
};

const data = {
  foo: 1,
  bar: "abc",
};

const validate = ajv.compile(schema);
const valid = validate(data);

if (!valid) console.log(validate.errors);

Community and Contributions

Ajv is a community-driven project with contributions from over 100 developers. It welcomes new contributors who can bring features beneficial to its users. The project is supported by a diverse group of sponsors including Mozilla, Microsoft, and Retool, making it a vibrant and evolving tool.

Support and Sponsorship

Sponsorships via GitHub and OpenCollective are crucial for ongoing maintenance and development efforts. Ajv is part of the Tidelift subscription platform, providing centralized support for open-source software users.

Conclusion

Ajv stands out as a leader in JSON validation, combining speed with thoroughness and adaptability. Its broad feature set and compliance with numerous standards make it a valuable asset for any developer working with JSON and JSON Schema.

This introduction offers a brief snapshot of Ajv's capabilities and should serve as a useful guide for both newcomers and experienced users looking to incorporate powerful JSON validation into their projects. For a more in-depth exploration, users are encouraged to visit the Ajv website.