Ajv: Another JSON schema validator
The fastest JSON schema 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.
Using version 7
Ajv version 7 has these new features:
- support of JSON Schema draft-2019-09 features:
unevaluatedProperties
and unevaluatedItems
, dynamic recursive references and other additional keywords. - NEW: support of JSON Type Definition RFC8927 (from v7.1.0)
- to reduce the mistakes in JSON schemas and unexpected validation results, strict mode is added - it prohibits ignored or ambiguous JSON Schema elements.
- to make code injection from untrusted schemas impossible, code generation is fully re-written to be safe and to allow code optimization (compiled schema code size is reduced by more than 10%).
- to simplify Ajv extensions, the new keyword API that is used by pre-defined keywords is available to user-defined keywords - it is much easier to define any keywords now, especially with subschemas. ajv-keywords package was updated to use the new API (in v4.0.0)
- schemas are compiled to ES6 code (ES5 code generation is also supported with an option).
- to improve reliability and maintainability the code is migrated to TypeScript.
Please note:
- the support for JSON-Schema draft-04 is removed - if you have schemas using "id" attributes you have to replace them with "$id" (or continue using Ajv v6 that will be supported until 02/28/2021).
- all formats are separated to ajv-formats package - they have to be explicitly added if you use them.
See release notes for the details.
To install the new version:
npm install ajv
See Getting started for code example.
Contributing
100+ people contributed to Ajv. You are very welcome to join by implementing new features that are valuable to many users and by improving documentation.
Please do not be disappointed if your suggestion is not accepted - it is important to maintain the balance between the library size, performance and functionality. If it seems that a feature would benefit only a small number of users, its addition may be delayed until there is more support from the users community - so please submit the issue first to explain why this feature is important.
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 review Contributing guidelines and Code components.
Contents
Mozilla MOSS grant and OpenJS Foundation
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.
Performance
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:
Features
Install
To install version 7:
npm install ajv
Getting started
Try it in the Node.js REPL: https://runkit.com/npm/ajv
In JavaScript:
import Ajv from "ajv"
const Ajv = require("ajv").default
const ajv = new Ajv()
const validate = ajv.compile(schema)
const valid = validate(data)
if (!valid) console.log(validate.errors)
In TypeScript:
import Ajv, {JSONSchemaType, DefinedError} from "ajv"
const ajv = new Ajv()
type MyData = {foo: number}
const schema: JSONSchemaType<MyData> = {
type: "object",
properties: {
foo: {type: "number", minimum: 0},
},
required: ["foo"],
additionalProperties: false,
}
const validate = ajv.compile(schema)
const data: any = {foo: 1}
if (validate(data)) {
console.log(data.foo)
} else {
for (const err of validate.errors as DefinedError[]) {
switch (err.keyword) {
case "minimum":
console.log(err.params.limit)
break
}
}
}
With JSON Type Definition schema:
const Ajv = require("ajv").default
const ajv = new Ajv()
const schema = {
properties: {
foo: {type: "float64"},
},
}
const validate = ajv.compile(schema)
const valid = validate({foo: 1})
if (!valid) console.log(validate.errors)
const valid1 = validate(1)
const valid2 = validate({})
const valid3 = validate({foo: 1, bar: 2})
See this test for an advanced example, API reference and Options for more details.
Ajv compiles schemas to functions and caches them in all cases (using schema itself as a key for Map) or another function passed via options), so that the next time the same schema is used (not necessarily the same object instance) it won't be compiled again.
The best performance is achieved when using compiled functions returned by compile
or getSchema
methods (there is no additional function call).
Please note: every time a validation function or ajv.validate
are called errors
property is overwritten. You need to copy errors
array reference to another variable if you want to use it later (e.g., in the callback). See Validation errors
Using in browser
See Content Security Policy to decide the best approach how to use Ajv in the browser.
Whether you use Ajv or compiled schemas, it is recommended that you bundle them together with your code.
If you need to use Ajv in several bundles you can create a separate UMD bundles using npm run bundle
script.
Then you need to load Ajv with support of JSON Schema draft-07 in the browser:
<script src="bundle/ajv7.min.js"></script>
<script>
;(function () {
const Ajv = window.ajv7.default
const ajv = new Ajv()
})()
</script>
To load the bundle that supports JSON Schema draft-2019-09:
<script src="bundle/ajv2019.min.js"></script>
<script>
;(function () {
const Ajv = window.ajv2019.default
const ajv = new Ajv()
})()
</script>
To load the bundle that supports JSON Type Definition:
<script src="bundle/ajvJTD.min.js"></script>
<script>
;(function () {
const Ajv = window.ajvJTD.default
const ajv = new Ajv()
})()
</script>
This bundle can be used with different module systems; it creates global ajv
(or ajv2019
) if no module system is found.
The browser bundle is available on cdnjs.
Please note: some frameworks, e.g. Dojo, may redefine global require in a way that is not compatible with CommonJS module format. In this case Ajv bundle has to be loaded before the framework and then you can use global ajv
(see issue #234).
Choosing schema language
Both JSON Schema and JSON Type Definition are cross-platform specifications with implementations in multiple programming languages that help you define the shape and requirements to your JSON data.
This section compares their pros/cons to help decide which specification fits your application better.
JSON Schema
- Pros
- Wide specification adoption.
- Used as part of OpenAPI specification.
- Support of complex validation scenarios:
- untagged unions and boolean logic
- conditional schemas and dependencies
- restrictions on the number ranges and the size of strings, arrays and objects
- semantic validation with formats, patterns and content keywords
- distribute strict record definitions across multiple schemas (with unevaluatedProperties)
- Can be effectively used for validation of any JavaScript objects and configuration files.
- Cons
- Defines the collection of restrictions on the data, rather than the shape of the data.
- No standard support for tagged unions.
- Complex and error prone for the new users (Ajv has strict mode to compensate for it, but it is not cross-platform).
- Some parts of specification are difficult to implement, creating the risk of implementations divergence:
- reference resolution model
- unevaluatedProperties/unevaluatedItems
- dynamic recursive references
- Internet draft status (rather than RFC)
See JSON Schema for the list of defined keywords.
JSON Type Definition
- Pros:
- Aligned with type systems of many languages - can be used to generate type definitions and efficient parsers and serializers to/from these types.
- Very simple, enforcing the best practices for cross-platform JSON API modelling.
- Simple to implement, ensuring consistency across implementations.
- Defines the shape of JSON data via strictly defined schema forms (rather than the collection of restrictions).
- Effective support for tagged unions.
- Designed to protect against user mistakes.
- Approved as RFC8927
- Cons:
- Limited, compared with JSON Schema - no support for untagged unions*, conditionals, references between different schema files**, etc.
- No meta-schema in the specification*.
- Brand new - limited industry adoption (as of January 2021).
* Ajv defines meta-schema for JTD schemas and non-standard keyword "union" that can be used inside "metadata" object.
** You can still combine schemas from multiple files in the application code.
See JSON Type Definition for the list of defined schema forms.
Using in ES5 environment
You need to:
- recompile Typescript to ES5 target - it is set to 2018 in the bundled compiled code.
- generate ES5 validation code:
const ajv = new Ajv({code: {es5: true}})
See Advanced options.
Command line interface
CLI is available as a separate npm package ajv-cli. It supports:
- compiling JSON Schemas to test their validity
- generating standalone validation code that exports validation function(s) to be used without Ajv
- migrating schemas to draft-07 and draft-2019-09 (using json-schema-migrate)
- validating data file(s) against JSON Schema
- testing expected validity of data against JSON Schema
- referenced schemas
- user-defined meta-schemas, validation keywords and formats
- files in JSON, JSON5, YAML, and JavaScript format
- all Ajv options
- reporting changes in data after validation in JSON-patch format
Extending Ajv
User defined keywords
See section in data validation and the detailed guide.
Plugins
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:
- it exports a function that accepts ajv instance as the first parameter - it allows using plugins with ajv-cli.
- this function returns the same instance to allow chaining.
- this function can accept an optional configuration as the second parameter.
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.
Related packages
- ajv-bsontype - plugin to validate mongodb's bsonType formats
- ajv-cli - command line interface
- ajv-formats - formats defined in JSON Schema specification
- ajv-errors - plugin for defining error messages in the schema
- ajv-i18n - internationalised error messages
- ajv-istanbul - plugin to instrument generated validation code to measure test coverage of your schemas
- ajv-keywords - plugin with additional validation keywords (select, typeof, etc.)
- ajv-merge-patch - plugin with keywords $merge and $patch
- ajv-formats-draft2019 - format validators for draft2019 that aren't included in ajv-formats (ie.
idn-hostname
, idn-email
, iri
, iri-reference
and duration
)
Some packages using Ajv
Changes history
See https://github.com/ajv-validator/ajv/releases
Please note: Changes in version 7.0.0
Version 6.0.0.
Code of conduct
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.
Security contact
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.
Open-source software support
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.
License
MIT