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The not keyword validates an instance by inverting the validation result of its subschema. An instance is valid if it fails to validate against the specified schema.

​
Syntax

{
  "not": { /* schema */ }
}
The value must be a valid JSON Schema.

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Behavior

An instance is valid against not if and only if it fails to validate successfully against the schema defined by this keyword.
  • The subschema is evaluated normally
  • The validation result is inverted (negated)
  • If the subschema passes, not fails
  • If the subschema fails, not passes
  • No annotations are produced by not

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Examples

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Exclude Specific Values

Reject a particular value: 
{
  "type": "string",
  "not": {
    "const": "forbidden"
  }
}
Valid: "hello", "world", "anything else"
Invalid: "forbidden"

​
Exclude Specific Types

Reject instances of a certain type: 
{
  "not": {
    "type": "null"
  }
}
Valid: "hello", 42, true, [], {}
Invalid: null

​
Exclude Pattern Matches

Reject strings matching a pattern: 
{
  "type": "string",
  "not": {
    "pattern": "^test"
  }
}
Valid: "production", "development"
Invalid: "test", "testing", "test-env"

​
Exclude Properties

Reject objects with specific properties: 
{
  "type": "object",
  "not": {
    "required": ["deprecated"]
  }
}
Valid: 
{ "name": "active" }
{ "id": 123 }
{}
Invalid: 
{ "deprecated": true, "name": "old" }

​
Exclude Number Ranges

Reject numbers in a specific range: 
{
  "type": "number",
  "not": {
    "minimum": 10,
    "maximum": 20
  }
}
Valid: 5, 9, 21, 100
Invalid: 10, 15, 20

​
Reject Empty Strings

Require non-empty strings: 
{
  "type": "string",
  "not": {
    "maxLength": 0
  }
}
Valid: "hello", "x"
Invalid: ""

​
Exclude Array Sizes

Reject arrays with specific lengths: 
{
  "type": "array",
  "not": {
    "minItems": 0,
    "maxItems": 0
  }
}
Valid: [1], [1, 2, 3]
Invalid: []

​
Complex Exclusions

Reject objects matching a complex pattern: 
{
  "type": "object",
  "not": {
    "allOf": [
      {
        "properties": {
          "status": { "const": "active" }
        },
        "required": ["status"]
      },
      {
        "properties": {
          "deleted": { "const": true }
        },
        "required": ["deleted"]
      }
    ]
  }
}
This rejects objects that are both active and deleted (an invalid state). Valid: 
{ "status": "active" }
{ "deleted": true }
{ "status": "inactive", "deleted": true }
Invalid: 
{ "status": "active", "deleted": true }

​
Enforce Constraints

Combine with other keywords to enforce rules: 
{
  "type": "object",
  "properties": {
    "age": { "type": "integer" },
    "minor": { "type": "boolean" }
  },
  "if": {
    "properties": {
      "age": { "minimum": 18 }
    },
    "required": ["age"]
  },
  "then": {
    "not": {
      "properties": {
        "minor": { "const": true }
      },
      "required": ["minor"]
    }
  }
}
This ensures that if age ≥ 18, minor cannot be true.

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Common Use Cases

  • Value exclusion: Reject specific disallowed values
  • Type restriction: Exclude certain types
  • Pattern rejection: Reject strings matching unwanted patterns
  • Property prohibition: Disallow specific object properties
  • Range exclusion: Reject values in forbidden ranges
  • State validation: Prevent invalid state combinations

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Notes

  • not is purely an assertion keyword; it never produces annotations
  • Boolean schema false is equivalent to { "not": {} } (always fails)
  • Boolean schema true is equivalent to { "not": false } (always passes)
  • Use with caution: negation can make schemas harder to understand
  • Validation error messages for not may be less intuitive
  • Double negation (not containing not) is valid but should be avoided for clarity

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Best Practices

  • Provide clear descriptions when using not to help schema consumers understand what is being rejected
  • Consider whether positive assertions might be clearer than negative ones
  • Use not sparingly and only when exclusion logic is truly necessary
  • Combine with if/then/else for complex conditional validation

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