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JSON Schema is a specification for JSON based format for defining the structure of JSON data. It was written under IETF draft which expired in 2011. JSON Schema −
- Describes your existing data format.
- Clear, human- and machine-readable documentation.
- Complete structural validation, useful for automated testing.
- Complete structural validation, validating client-submitted data.
JSON Schema Validation Libraries
There are several validators currently available for different programming languages. Currently the most complete and compliant JSON Schema validator available is JSV.
| Languages | Libraries |
|---|---|
| C | WJElement (LGPLv3) |
| Java | json-schema-validator (LGPLv3) |
| .NET | Json.NET (MIT) |
| ActionScript 3 | Frigga (MIT) |
| Haskell | aeson-schema (MIT) |
| Python | Jsonschema |
| Ruby | autoparse (ASL 2.0); ruby-jsonschema (MIT) |
| PHP | php-json-schema (MIT). json-schema (Berkeley) |
| JavaScript | Orderly (BSD); JSV; json-schema; Matic (MIT); Dojo; Persevere (modified BSD or AFL 2.0); schema.js. |
JSON Schema Example
Given below is a basic JSON schema, which covers a classical product catalog description −
{
"$schema": "http://json-schema.org/draft-04/schema#",
"title": "Product",
"description": "A product from Acme''s catalog",
"type": "object",
"properties": {
"id": {
"description": "The unique identifier for a product",
"type": "integer"
},
"name": {
"description": "Name of the product",
"type": "string"
},
"price": {
"type": "number",
"minimum": 0,
"exclusiveMinimum": true
}
},
"required": ["id", "name", "price"]
}
Let”s the check various important keywords that can be used in this schema −
| Sr.No. | Keyword & Description |
|---|---|
| 1 |
$schema The $schema keyword states that this schema is written according to the draft v4 specification. |
| 2 |
title You will use this to give a title to your schema. |
| 3 |
description A little description of the schema. |
| 4 |
type The type keyword defines the first constraint on our JSON data: it has to be a JSON Object. |
| 5 |
properties Defines various keys and their value types, minimum and maximum values to be used in JSON file. |
| 6 |
required This keeps a list of required properties. |
| 7 |
minimum This is the constraint to be put on the value and represents minimum acceptable value. |
| 8 |
exclusiveMinimum If “exclusiveMinimum” is present and has boolean value true, the instance is valid if it is strictly greater than the value of “minimum”. |
| 9 |
maximum This is the constraint to be put on the value and represents maximum acceptable value. |
| 10 |
exclusiveMaximum If “exclusiveMaximum” is present and has boolean value true, the instance is valid if it is strictly lower than the value of “maximum”. |
| 11 |
multipleOf A numeric instance is valid against “multipleOf” if the result of the division of the instance by this keyword”s value is an integer. |
| 12 |
maxLength The length of a string instance is defined as the maximum number of its characters. |
| 13 |
minLength The length of a string instance is defined as the minimum number of its characters. |
| 14 |
pattern A string instance is considered valid if the regular expression matches the instance successfully. |
You can check a http://json-schema.org for the complete list of keywords that can be used in defining a JSON schema. The above schema can be used to test the validity of the following JSON code −
[
{
"id": 2,
"name": "An ice sculpture",
"price": 12.50,
},
{
"id": 3,
"name": "A blue mouse",
"price": 25.50,
}
]
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