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The string type is used for strings of text. It may contain Unicode characters.

In Python, “string” is analogous to the unicode type on Python 2.x, and the str type on Python 3.x.
In Ruby, “string” is analogous to the String type.
{ "type": "string" }
"This is a string"

Unicode characters:

"Déjà vu"


The length of a string can be constrained using the minLength and maxLength keywords. For both keywords, the value must be a non-negative number.

  "type": "string",
  "minLength": 2,
  "maxLength": 3

Regular Expressions

The pattern keyword is used to restrict a string to a particular regular expression. The regular expression syntax is the one defined in JavaScript (ECMA 262 specifically). See Regular Expressions for more information.


When defining the regular expressions, it’s important to note that the string is considered valid if the expression matches anywhere within the string. For example, the regular expression "p" will match any string with a p in it, such as "apple" not just a string that is simply "p". Therefore, it is usually less confusing, as a matter of course, to surround the regular expression in ^...$, for example, "^p$", unless there is a good reason not to do so.

The following example matches a simple North American telephone number with an optional area code:

   "type": "string",
   "pattern": "^(\\([0-9]{3}\\))?[0-9]{3}-[0-9]{4}$"
"(888)555-1212 ext. 532"


The format keyword allows for basic semantic validation on certain kinds of string values that are commonly used. This allows values to be constrained beyond what the other tools in JSON Schema, including Regular Expressions can do.


JSON Schema implementations are not required to implement this part of the specification, and many of them do not.

There is a bias toward networking-related formats in the JSON Schema specification, most likely due to its heritage in web technologies. However, custom formats may also be used, as long as the parties exchanging the JSON documents also exchange information about the custom format types. A JSON Schema validator will ignore any format type that it does not understand.

Built-in formats

The following is the list of formats specified in the JSON Schema specification.