The ajv npm package is a fast JSON Schema validator that allows you to validate JSON data against a JSON schema. It supports the latest JSON Schema draft-07 and has several extensions. It can be used for data validation, data sanitization, and to ensure that JSON documents comply with a predefined schema.
Validate data against a JSON Schema
This feature allows you to compile a JSON Schema and use it to validate JSON data. If the data does not conform to the schema, the errors can be logged or handled as needed.
{"const Ajv = require('ajv');
const ajv = new Ajv();
const schema = {
"type": "object",
"properties": {
"foo": {"type": "integer"},
"bar": {"type": "string"}
},
"required": ["foo"]
};
const validate = ajv.compile(schema);
const valid = validate({foo: 1, bar: 'abc'});
if (!valid) console.log(validate.errors);"}Add custom keywords
Ajv allows you to define custom keywords for a JSON Schema, which can be used to create custom validation rules that are not defined in the JSON Schema specification.
{"const Ajv = require('ajv');
const ajv = new Ajv();
ajv.addKeyword('even', {
validate: function(schema, data) {
return data % 2 === 0;
}
});
const schema = {"even": true};
const validate = ajv.compile(schema);
const valid = validate(2); // true
const invalid = validate(3); // false"}Asynchronous validation
Ajv supports asynchronous schema compilation, which is useful when your JSON Schema depends on other schemas that need to be fetched remotely.
{"const Ajv = require('ajv');
const ajv = new Ajv({loadSchema: loadExternalSchema});
// Assume loadExternalSchema is a function that loads a schema asynchronously
ajv.compileAsync(schema).then(function(validate) {
const valid = validate(data);
if (!valid) console.log(validate.errors);
}).catch(function(err) {
console.error('Failed to compile schema:', err);
});"}Joi is a powerful schema description language and data validator for JavaScript. Unlike ajv, which focuses on JSON Schema, Joi allows you to create validation schemas using a fluent API. It is often used for validating data in REST APIs.
Tiny Validator (tv4) is a small and fast JSON Schema (v4) validator. It is less feature-rich compared to ajv and does not support the latest JSON Schema specifications, but it is suitable for simple validation tasks.
The jsonschema package is another validator for JSON Schema that supports draft-04/06/07. It is not as fast as ajv but provides a straightforward API for validating JSON data against schemas.
Super fast JSON validator for Node.js and browser.
Supports JSON Schema draft-06/07/2019-09 (draft-04 is supported in version 6) and JSON Type Definition RFC8927.
Ajv version 7 has these new features:
unevaluatedProperties and unevaluatedItems, dynamic recursive references and other additional keywords.Please note:
See release notes for the details.
To install the new version:
npm install ajv
See Getting started for code example.
More than 100 people contributed to Ajv, and we would love to have you join the development. We welcome implementing new features that will benefit many users and ideas to improve our documentation.
At Ajv, we are committed to creating more equitable and inclusive spaces for our community and team members to contribute to discussions that affect both this project and our ongoing work in the open source ecosystem.
We strive to create an environment of respect and healthy discourse by setting standards for our interactions and we expect it from all members of our community - from long term project member to first time visitor. For more information, review our code of conduct and values.
We value conscious curation of our library size, and balancing performance and functionality. To that end, we cannot accept every suggestion. When evaluating pull requests we consider:
To help us evaluate and understand, when you submit an issue and pull request:
Please include documentation and test coverage with any new feature implementations.
To run tests:
npm install
git submodule update --init
npm test
npm run build - compiles typescript to dist folder.
Please also review Contributing guidelines and Code components.
Ajv has been awarded a grant from Mozilla’s Open Source Support (MOSS) program in the “Foundational Technology” track! It will sponsor the development of Ajv support of JSON Schema version 2019-09 and of JSON Type Definition (RFC8927).
Ajv also joined OpenJS Foundation – having this support will help ensure the longevity and stability of Ajv for all its users.
This blog post has more details.
I am looking for the long term maintainers of Ajv – working with ReadySet, also sponsored by Mozilla, to establish clear guidelines for the role of a "maintainer" and the contribution standards, and to encourage a wider, more inclusive, contribution from the community.
Since I asked to support Ajv development 40 people and 6 organizations contributed via GitHub and OpenCollective - this support helped receiving the MOSS grant!
Your continuing support is very important - the funds will be used to develop and maintain Ajv once the next major version is released.
Please sponsor Ajv via:
Thank you.
Ajv generates code to turn JSON Schemas into super-fast validation functions that are efficient for v8 optimization.
Currently Ajv is the fastest and the most standard compliant validator according to these benchmarks:
Performance of different validators by json-schema-benchmark:
addSchema or compiled to be available)type keywordsconst, contains, propertyNames and if/then/elsetrue/false as a schema to always pass/fail).To install version 7:
npm install ajv
Try it in the Node.js REPL: https://runkit.com/npm/ajv
In JavaScript:
// or ESM/TypeScript import
import Ajv from "ajv"
// Node.js require:
const Ajv = require("ajv").default
const ajv = new Ajv() // options can be passed, e.g. {allErrors: true}
const validate = ajv.compile(schema)
const valid = validate(data)
if (!valid) console.log(validate.errors)
See more examples in Guide: getting started
See section in data validation and the detailed guide.
Ajv can be extended with plugins that add keywords, formats or functions to process generated code. When such plugin is published as npm package it is recommended that it follows these conventions:
You can import Plugin interface from ajv if you use Typescript.
If you have published a useful plugin please submit a PR to add it to the next section.
idn-hostname, idn-email, iri, iri-reference and duration)See https://github.com/ajv-validator/ajv/releases
Please note: Changes in version 7.0.0
Please review and follow the Code of conduct.
Please report any unacceptable behaviour to ajv.validator@gmail.com - it will be reviewed by the project team.
To report a security vulnerability, please use the Tidelift security contact. Tidelift will coordinate the fix and disclosure. Please do NOT report security vulnerabilities via GitHub issues.
Ajv is a part of Tidelift subscription - it provides a centralised support to open-source software users, in addition to the support provided by software maintainers.
FAQs
Another JSON Schema Validator
The npm package ajv receives a total of 94,134,291 weekly downloads. As such, ajv popularity was classified as popular.
We found that ajv demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 2 open source maintainers collaborating on the project.
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