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The default keyword specifies a default JSON value that can be used when an instance value is not provided. It is commonly used in configuration schemas, form generation, and API documentation.

​
Syntax

The value of default can be of any type, including null. There are no restrictions on the value. 
{
  "default": <any JSON value>
}

​
Purpose

The default keyword is a metadata annotation that:
  • Supplies a default value when no value is provided
  • Helps tools generate forms with pre-filled values
  • Documents the recommended or typical value for a field
  • Can be used by implementations to fill in missing values
  • Has no effect on validation (it is purely informational)
  • Should be a valid value against the associated schema (recommended)

​
Behavior

When multiple occurrences of the default keyword are applicable to a single sub-instance, implementations should remove duplicates. Implementations may use the default value as an additional example for documentation purposes.

​
Examples

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Basic Default Values

{
  "type": "integer",
  "title": "Port",
  "description": "Server port number",
  "default": 8080,
  "minimum": 1,
  "maximum": 65535
}
The default port is 8080, which will be used if no port is specified.

​
String Default

{
  "type": "string",
  "title": "Environment",
  "enum": ["development", "staging", "production"],
  "default": "development"
}
Defaults to “development” environment when not specified.

​
Boolean Default

{
  "type": "boolean",
  "title": "Enable Logging",
  "description": "Enable detailed application logging",
  "default": true
}
Logging is enabled by default.

​
Object with Default Values

{
  "type": "object",
  "title": "Database Configuration",
  "properties": {
    "host": {
      "type": "string",
      "default": "localhost"
    },
    "port": {
      "type": "integer",
      "default": 5432
    },
    "database": {
      "type": "string",
      "default": "myapp"
    },
    "ssl": {
      "type": "boolean",
      "default": false
    }
  }
}
Each property has its own default value, providing a complete default configuration.

​
Array Default

{
  "type": "array",
  "title": "Allowed Origins",
  "description": "CORS allowed origins",
  "items": {
    "type": "string"
  },
  "default": ["http://localhost:3000"]
}
Defaults to allowing localhost origin.

​
Null Default

{
  "type": ["string", "null"],
  "title": "Middle Name",
  "description": "User's middle name (optional)",
  "default": null
}
Defaults to null when no middle name is provided.

​
Configuration Schema

{
  "type": "object",
  "title": "Application Settings",
  "properties": {
    "server": {
      "type": "object",
      "properties": {
        "port": {
          "type": "integer",
          "default": 3000
        },
        "host": {
          "type": "string",
          "default": "0.0.0.0"
        }
      }
    },
    "logging": {
      "type": "object",
      "properties": {
        "level": {
          "type": "string",
          "enum": ["debug", "info", "warn", "error"],
          "default": "info"
        },
        "format": {
          "type": "string",
          "enum": ["json", "text"],
          "default": "json"
        }
      }
    },
    "cache": {
      "type": "object",
      "properties": {
        "enabled": {
          "type": "boolean",
          "default": true
        },
        "ttl": {
          "type": "integer",
          "description": "Cache time-to-live in seconds",
          "default": 3600
        }
      }
    }
  }
}
A complete configuration schema with sensible defaults for all settings.

​
Pagination Parameters

{
  "type": "object",
  "title": "Pagination Options",
  "properties": {
    "page": {
      "type": "integer",
      "description": "Page number to retrieve",
      "minimum": 1,
      "default": 1
    },
    "pageSize": {
      "type": "integer",
      "description": "Number of items per page",
      "minimum": 1,
      "maximum": 100,
      "default": 20
    },
    "sortBy": {
      "type": "string",
      "description": "Field to sort by",
      "default": "createdAt"
    },
    "sortOrder": {
      "type": "string",
      "enum": ["asc", "desc"],
      "default": "desc"
    }
  }
}
API pagination with sensible defaults for common use cases.

​
Theme Configuration

{
  "type": "object",
  "title": "Theme Settings",
  "properties": {
    "mode": {
      "type": "string",
      "enum": ["light", "dark", "auto"],
      "default": "auto"
    },
    "primaryColor": {
      "type": "string",
      "pattern": "^#[0-9a-fA-F]{6}$",
      "default": "#007bff"
    },
    "fontSize": {
      "type": "string",
      "enum": ["small", "medium", "large"],
      "default": "medium"
    },
    "borderRadius": {
      "type": "integer",
      "description": "Border radius in pixels",
      "minimum": 0,
      "default": 4
    }
  }
}
UI theme settings with reasonable defaults.

​
Feature Flags

{
  "type": "object",
  "title": "Feature Flags",
  "properties": {
    "enableBetaFeatures": {
      "type": "boolean",
      "description": "Enable experimental beta features",
      "default": false
    },
    "enableAnalytics": {
      "type": "boolean",
      "description": "Enable usage analytics tracking",
      "default": true
    },
    "enableNotifications": {
      "type": "boolean",
      "description": "Enable push notifications",
      "default": true
    },
    "maxUploadSize": {
      "type": "integer",
      "description": "Maximum file upload size in MB",
      "minimum": 1,
      "maximum": 100,
      "default": 10
    }
  }
}
Feature flags with safe defaults.

​
Retry Configuration

{
  "type": "object",
  "title": "Retry Policy",
  "properties": {
    "maxRetries": {
      "type": "integer",
      "description": "Maximum number of retry attempts",
      "minimum": 0,
      "maximum": 10,
      "default": 3
    },
    "initialDelay": {
      "type": "integer",
      "description": "Initial delay in milliseconds",
      "minimum": 100,
      "default": 1000
    },
    "maxDelay": {
      "type": "integer",
      "description": "Maximum delay in milliseconds",
      "minimum": 1000,
      "default": 30000
    },
    "backoffMultiplier": {
      "type": "number",
      "description": "Exponential backoff multiplier",
      "minimum": 1,
      "default": 2
    }
  }
}
Retry policy with standard exponential backoff defaults.

​
Search Options

{
  "type": "object",
  "title": "Search Parameters",
  "properties": {
    "query": {
      "type": "string",
      "description": "Search query string"
    },
    "caseSensitive": {
      "type": "boolean",
      "default": false
    },
    "matchWholeWord": {
      "type": "boolean",
      "default": false
    },
    "includeArchived": {
      "type": "boolean",
      "default": false
    },
    "maxResults": {
      "type": "integer",
      "minimum": 1,
      "maximum": 1000,
      "default": 100
    }
  },
  "required": ["query"]
}
Search configuration with user-friendly defaults.

​
Best Practices

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Use Valid Defaults

Ensure default values validate against the schema: 
{
  "type": "integer",
  "minimum": 1,
  "maximum": 100,
  "default": 10
}

​
Choose Safe Defaults

Select defaults that are safe for production use: 
{
  "type": "boolean",
  "title": "Debug Mode",
  "description": "Enable debug mode (should be false in production)",
  "default": false
}

​
Document Default Behavior

Combine default with description to explain the default choice: 
{
  "type": "integer",
  "title": "Connection Timeout",
  "description": "Connection timeout in milliseconds. Default is 30 seconds, which is suitable for most network conditions.",
  "minimum": 1000,
  "default": 30000
}

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