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JSON Forms supports both JSON Schema Draft 4 and Draft 7. The main JsonSchema type is a union of both versions.

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JsonSchema

Union type for JSON Schema Draft 4 and Draft 7.
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JsonSchema
JsonSchema4 | JsonSchema7
Main type that accepts either JSON Schema Draft 4 or Draft 7 schemas.

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JsonSchema7

JSON Schema Draft 7 specification interface.

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Schema metadata

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$id
string
Schema identifier. Tells references where the root of the document is located.
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$schema
string
Meta-schema URL. Recommended to include in the root of any JSON Schema.
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$ref
string
Reference to another schema or schema definition.
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title
string
Human-readable title of the schema.
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description
string
Detailed description of the schema.
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default
any
Default value for the data represented by this schema.

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Type definition

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type
string | string[]
The basic type of this schema. Can be one of: string, number, integer, object, array, boolean, null, or an array of these types.
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enum
any[]
Enumerates the allowed values for this schema.
{
  "type": "string",
  "enum": ["red", "green", "blue"]
}
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const
any
Specifies a single constant value that the data must match.

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Number validation

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multipleOf
number
The value must be a multiple of this number (e.g., 10 is a multiple of 5).
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maximum
number
Maximum value allowed (inclusive).
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exclusiveMaximum
number
Maximum value allowed (exclusive). Value must be less than this number.
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minimum
number
Minimum value allowed (inclusive).
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exclusiveMinimum
number
Minimum value allowed (exclusive). Value must be greater than this number.

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String validation

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maxLength
number
Maximum length of the string.
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minLength
number
Minimum length of the string.
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pattern
string
Regular expression pattern that the string must match.
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format
string
String format identifier (e.g., date, time, date-time, email, uri).

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Array validation

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items
JsonSchema7 | JsonSchema7[]
Schema for array items. Can be a single schema or an array of schemas for tuple validation.
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additionalItems
boolean | JsonSchema7
Schema for additional items beyond those defined in items array.
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maxItems
number
Maximum number of items in the array.
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minItems
number
Minimum number of items in the array.
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uniqueItems
boolean
Whether all items in the array must be unique.
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contains
JsonSchema7
Schema that at least one array item must match.

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Object validation

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properties
{ [property: string]: JsonSchema7 }
Map of property names to their schemas.
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patternProperties
{ [pattern: string]: JsonSchema7 }
Map of regex patterns to schemas. Properties matching the pattern must validate against the schema.
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additionalProperties
boolean | JsonSchema7
Schema for properties not defined in properties or patternProperties. If false, no additional properties are allowed.
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required
string[]
Array of property names that must be present.
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propertyNames
JsonSchema7
Schema that all property names must match.
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maxProperties
number
Maximum number of properties allowed.
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minProperties
number
Minimum number of properties required.
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dependencies
{ [key: string]: JsonSchema7 | string[] }
Defines dependencies between properties. Value can be an array of required property names or a schema that must validate when the key property is present.

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Schema composition

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allOf
JsonSchema7[]
Data must validate against all of the schemas in this array.
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anyOf
JsonSchema7[]
Data must validate against at least one of the schemas in this array.
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oneOf
JsonSchema7[]
Data must validate against exactly one of the schemas in this array.
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not
JsonSchema7
Data must not validate against this schema.

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Conditional schemas

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if
JsonSchema7
Conditional schema. If data validates against this schema, apply the then schema.
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then
JsonSchema7
Schema to apply if the if condition is true.
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else
JsonSchema7
Schema to apply if the if condition is false.

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Schema reuse

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definitions
{ [key: string]: JsonSchema7 }
Container for reusable schema definitions. Reference with $ref.
{
  "definitions": {
    "address": {
      "type": "object",
      "properties": {
        "street": { "type": "string" },
        "city": { "type": "string" }
      }
    }
  },
  "type": "object",
  "properties": {
    "billingAddress": { "$ref": "#/definitions/address" }
  }
}

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Additional properties

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readOnly
boolean
Indicates the value should not be modified.
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writeOnly
boolean
Indicates the value may be set but should not be retrieved.
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examples
any[]
Array of example values for documentation.
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errorMessage
any
Custom error message for validation failures.

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JsonSchema4

JSON Schema Draft 4 specification interface. Similar to Draft 7 with key differences:

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Key differences from Draft 7

  • Uses id instead of $id for schema identifier
  • exclusiveMaximum and exclusiveMinimum are boolean instead of number
  • Does not support: const, contains, propertyNames, if/then/else, readOnly, writeOnly, examples
Most JSON Forms projects use JSON Schema Draft 7. Draft 4 support is maintained for backward compatibility.

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Usage example

import { JsonSchema } from '@jsonforms/core';

const schema: JsonSchema = {
  type: 'object',
  properties: {
    name: {
      type: 'string',
      minLength: 3,
      description: 'User name'
    },
    age: {
      type: 'integer',
      minimum: 0,
      maximum: 120
    },
    email: {
      type: 'string',
      format: 'email'
    },
    role: {
      type: 'string',
      enum: ['admin', 'user', 'guest']
    }
  },
  required: ['name', 'email']
};

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