const

The const keyword restricts an instance to a single, specific value.

Syntax

The value of const may be of any type, including null.

{
  "const": value
}

Validation Rules

An instance validates successfully if its value is equal to the value specified in the const keyword. Equality is determined using the rules defined in the JSON Schema Core specification.

Relationship to enum

Using const is functionally equivalent to using enum with a single-element array:

{"const": "value"}

is equivalent to:

{"enum": ["value"]}

Examples

String Constant

{
  "const": "United States"
}

Valid instance:

"United States"

Invalid instances:

"united states"
"USA"
"US"

Numeric Constant

{
  "const": 42
}

Valid instance:

Invalid instances:

"42"
42.0
43

Boolean Constant

{
  "const": true
}

Valid instance:

true

Invalid instances:

false
"true"
1

Null Constant

{
  "const": null
}

Valid instance:

null

Invalid instances:

""
0
false

Object Constant

{
  "const": {
    "version": "1.0.0",
    "protocol": "https"
  }
}

Valid instance:

{
  "version": "1.0.0",
  "protocol": "https"
}

Invalid instances:

{"version": "1.0.0"}
{"version": "1.0.0", "protocol": "https", "extra": true}

Array Constant

{
  "const": [1, 2, 3]
}

Valid instance:

[1, 2, 3]

Invalid instances:

[1, 2]
[1, 2, 3, 4]
[3, 2, 1]

API Version

{
  "type": "object",
  "properties": {
    "apiVersion": {
      "const": "v2"
    },
    "data": {
      "type": "object"
    }
  },
  "required": ["apiVersion"]
}

This ensures all instances must use API version “v2”.

Use Cases

Enforcing specific API versions
Requiring exact configuration values
Discriminating between schema variants
Defining literal values in conditional schemas
Ensuring backwards compatibility by requiring specific field values

Core Keywords

Applicator Keywords

Validation Keywords

Meta-Data

Syntax

Validation Rules

Relationship to enum

Examples

String Constant

Numeric Constant

Boolean Constant

Null Constant

Object Constant

Array Constant

API Version

Use Cases

​Syntax

​Validation Rules

​Relationship to enum

​Examples

​String Constant

​Numeric Constant

​Boolean Constant

​Null Constant

​Object Constant

​Array Constant

​API Version

​Use Cases

Syntax

Validation Rules

Relationship to enum

Examples

String Constant

Numeric Constant

Boolean Constant

Null Constant

Object Constant

Array Constant

API Version

Use Cases