The most important keywords that can be used in this schema:

$schema

- The $schema keyword states that this schema is written according to the draft v4 specification

title

- the title of the schema

description

- the description of the schema

type

- defines the type of the JSON (object / array)

properties

- defines various keys and their value types, minimum and maximum values to be used in JSON file

required

- this keeps a list of required properties

minimum

- minimum acceptable value for the item

exclusiveMinimum

- If "exclusiveMinimum" is present and has boolean value true, the value must be greater than the value of "minimum"

maximum

- maximum acceptable value for the item

exclusiveMaximum

- If "exclusiveMaximum" is present and has boolean value true, the value must be lower than the value of "maximum"

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

maxLength

- the length of a string instance is defined as the maximum number of its characters

minLength

- the length of a string instance is defined as the minimum number of its characters

pattern

- a string instance is considered valid if the regular expression matches the instance successfully ... JSON schema example

{
  "$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",
      "minLength": 5,
      "maxLength": 20
    },
    "price": {
      "type": "number",
      "minimum": 0,
      "exclusiveMinimum": true
    }
  },
  "required": [
    "id",
    "name",
    "price"
  ]
}

JSON that the schema above belongs to:

{
    "id": 2,
    "name": "Lorem ipsum dolor si",
    "price": 0.5
}

If the JSON was:

{
    "id": 2.5,
    "name": "Lorem ipsum dolor sit amet",
    "price": -0.5
}

It would have the following errors:

- Invalid type. Expected Integer but got Number
- String 'Lorem ipsum dolor sit amet' exceeds maximum length of 20
- Float -0.5 is less than minimum value of 0

For validating the JSON with its schema, the resource below can be used

https://www.jsonschemavalidator.net/