What validation keywords I can use in JSON Schema to specifically validate JSON String values?

The current JSON Schema specification supports the following validation keywords to specifically validate JSON Strings values. They are not applied if the JSON instance is not a JSON String.

"maxLength" - If the JSON instance is a string, its length must be less than or equal to the given value. For example:

JSON Schema: 
{"maxLength": "5"}

Valid JSON instance:
"Hello!"

Valid JSON instance:
3.14159

Invalid JSON instance:
"Hello world!"

"minLength" - If the JSON instance is a string, its length must be greater than or equal to the given value. For example:

JSON Schema: 
{"minLength": "5"}

Valid JSON instance:
"Hello!"

Valid JSON instance:
3.14159

Invalid JSON instance:
"Hi!"

"pattern" - If the JSON instance is a string, it must result a match for the given regular expression. For example:

JSON Schema: 
{"pattern": ".*@.*"}

Valid JSON instance:
"help@fyicenter.com"

Valid JSON instance:
3.14159

Invalid JSON instance:
"Hello world!"

⇒ JSON Schema Validation for JSON Array Values

⇐ JSON Schema Validation for JSON Number Values

⇑ Introduction of JSON Schema

⇑⇑ JSON Tutorials