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.
One of the fastest JSON Schema validators for node.js and browser.
It uses precompiled doT templates to generate super-fast validating functions.
ajv implements full JSON Schema draft 4 standard:
addSchema or compiled to be available)ajv passes all the tests from JSON Schema Test Suite (apart from the one that requires that 1.0 is not an integer).
Benchmark of the test suite - json-schema-benchmark.
Same benchmark run on faster CPU with node 0.12.
Benchmark of individual test cases by z-schema.
npm install ajv
var Ajv = require('ajv');
var ajv = Ajv(); // options can be passed
var validate = ajv.compile(schema);
var valid = validate(data);
if (!valid) console.log(validate.errors);
or
// ...
var valid = ajv.validate(schema, data);
if (!valid) console.log(ajv.errors);
// ...
or
// ...
ajv.addSchema(schema, 'mySchema');
var valid = ajv.validate('mySchema', data);
if (!valid) console.log(ajv.errorsText());
// ...
ajv compiles schemas to functions and caches them in all cases (using stringified schema as a key - using json-stable-stringify), so that the next time the same schema is used (not necessarily the same object instance) it won't be compiled again.
You can require ajv directly from the code you browserify - in this case ajv will be a part of your bundle.
If you need to use ajv in several bundles you can create a separate browserified bundle using bin/create-bundle script (thanks to siddo420).
Then you need to load ajv in the browser:
<script src="ajv.bundle.js"></script>
Now you can use it as shown above - require will be global and you can require('ajv').
Ajv was tested with these browsers:
The following formats are supported for string validation with "format" keyword:
date and date-time validate ranges in full mode and only regexp in fast mode (see options).There are two modes of fomat validation: fast and full that affect all formats but ipv4 and ipv6. See Options for details.
You can add additional formats and replace any of the formats above using addFormat method.
You can find patterns used for format validation and the sources that were used in formats.js.
Create ajv instance.
All the instance methods below are bound to the instance, so they can be used without the instance.
Generate validating function and cache the compiled schema for future use.
Validating function returns boolean and has properties errors with the errors from the last validation (null if there were no errors) and schema with the reference to the original schema.
Unless the option validateSchema is false, the schema will be validated against meta-schema and if schema is invalid the error will be thrown. See options.
Validate data using passed schema (it will be compiled and cached).
Instead of the schema you can use the key that was previously passed to addSchema, the schema id if it was present in the schema or any previously resolved reference.
Validation errors will be available in the errors property of ajv instance (null if there were no errors).
Add and compile schema(s). It does the same as .compile with two differences:
array of schemas can be passed (schemas should have ids), the second parameter will be ignored.
key can be passed that can be used to reference the schema and will be used as the schema id if there is no id inside the schema. If the key is not passed, the schema id will be used as the key.
Once the schema added it and all the references inside it can be referenced in other schemas and used to validate data.
In the current version all the referenced schemas should be added before the schema that uses them is compiled, so the circular references are not supported.
Version 1.0 will only compile schemas when they are used the first time. The order of addition in this version is not important and it supports circular references. Try it from the branch if you need them and please report any issues.
By default schema is validated against meta-schema before it is compiled and if the schema does not pass validation the exception is thrown. This behaviour is controlled by validateSchema option.
Validates schema. This method should be used to validate schemas rather than validate due to the inconsistency of uri format in JSON-Schema standart.
By default this method is called automatically when the schema is added, so you rarely need to use it directly.
If schema doesn't have $schema property it is validated against draft 4 meta-schema (option meta should not be false).
If schema has $schema property then the schema with this id (should be previously added) is used to validate passed schema.
Errors will be available at ajv.errors.
Retrieve compiled schema previously added with addSchema by the key passed to addSchema or by its full reference (id). Returned validating function has schema property with the reference to the original schema.
Remove added/cached schema. Even if schema is referenced by other schemas it can be safely removed as dependent schemas have local references.
Schema can be removed using key passed to addSchema, it's full reference (id) or using actual schema object that will be stable-stringified to remove schema from cache.
Add custom format to validate strings. It can also be used to replace pre-defined formats for ajv instance.
Strings are converted to RegExp.
Function should return validation result as true or false.
Custom formats can be also added via formats option.
Returns the text with all errors in a String.
Options can have properties separator (string used to separate errors, ", " by default) and dataVar (the variable name that dataPaths are prefixed with, "data" by default).
false not to validate formats at all. E.g., 25:00:00 and 2015/14/33 will be invalid time and date in 'full' mode but it will be valid in 'fast' mode.addFormat method.addSchema(value, key) will be called for each schema in this object.$schema property in the schema can either be absent (draft-4 meta-schema will be used) or can be a reference to any previously added schema. If the validation fails, the exception is thrown. Pass "log" in this option to log error instead of throwing exception. Pass false to skip schema validation.uniqueItems keyword (true by default).false to use .length of strings that is faster, but gives "incorrect" lengths of strings with unicode pairs - each unicode pair is counted as two characters.npm install js-beautify to use this option. true or js-beautify options can be passed.put(key, value) and get(key).npm install
git submodule update --init
npm test
All validation functions are generated using doT templates in dot folder. Templates are precompiled so doT is not a run-time dependency.
bin/compile-dots to compile templates to dotjs folder
bin/watch-dots to automatically compile templates when files in dot folder change
bin/git-hook to install symbolic link to pre-commit hook that will compile templates and run tests.
Errors for "required" keyword validation include missing properties
Better references resolution in schemas without IDs
cache option and removeSchema method
doT is no longer a run-time dependency
ajv can be used in the browser (with browserify)
Schemas are validated against meta-schema before compilation
Custom formats support.
Errors are set to null if there are no errors (previously empty array).
FAQs
Another JSON Schema Validator
The npm package ajv receives a total of 106,498,709 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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