string type is used for strings of text. It may contain Unicode characters.
unicodetype on Python
The length of a string can be constrained using the
maxLength keywords. For both keywords, the value must be a
pattern keyword is used to restrict a string to a particular
regular expression. The regular expression syntax is the one defined in
specifically) with Unicode support. 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
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,
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:
format keyword allows for basic semantic identification of certain
kinds of string values that are commonly used. For example, because JSON
doesn't have a "DateTime" type, dates need to be encoded as strings.
format allows the schema author to indicate that the string value
should be interpreted as a date. By default,
format is just an
annotation and does not effect validation.
Optionally, validator implementations can provide a configuration option
format to function as an assertion rather than just an
annotation. That means that validation will fail if, for example, a
value with a
date format isn't in a form that can be parsed as a
date. This can allow values to be constrained beyond what the other
tools in JSON Schema, including Regular Expressions can
Implementations may provide validation for only a subset of the built-in
formats or do partial validation for a given format. For example, some
implementations may consider a string an email if it contains a
while others might do additional checks for other aspects of a well
formed email address.
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.
The following is the list of formats specified in the JSON Schema specification.
Dates and times¶
"date-time": Date and time together, for example,
"time":New in draft 7Time, for example,
"date":New in draft 7Date, for example,
"duration":New in draft 2019-09A duration as defined by the ISO 8601 ABNF for "duration". For example,
P3Dexpresses a duration of 3 days.
"email": Internet email address, see RFC 5321, section 4.1.2.
"idn-email":New in draft 7The internationalized form of an Internet email address, see RFC 6531.
"hostname": Internet host name, see RFC 1123, section 2.1.
"idn-hostname":New in draft 7An internationalized Internet host name, see RFC5890, section 126.96.36.199.
"ipv4": IPv4 address, according to dotted-quad ABNF syntax as defined in RFC 2673, section 3.2.
"ipv6": IPv6 address, as defined in RFC 2373, section 2.2.
"uuid":New in draft 2019-09A Universally Unique Identifier as defined by RFC 4122. Example:
"uri": A universal resource identifier (URI), according to RFC3986.
"uri-reference":New in draft 6A URI Reference (either a URI or a relative-reference), according to RFC3986, section 4.1.
"iri":New in draft 7The internationalized equivalent of a "uri", according to RFC3987.
"iri-reference":New in draft 7The internationalized equivalent of a "uri-reference", according to RFC3987
If the values in the schema have the ability to be relative to a
particular source path (such as a link from a webpage), it is generally
better practice to use
"uri" should only be used when the path
must be absolute.
"uri-template":New in draft 6A URI Template (of any level) according to RFC6570. If you don't already know what a URI Template is, you probably don't need this value.
"json-pointer":New in draft 6A JSON Pointer, according to RFC6901. There is more discussion on the use of JSON Pointer within JSON Schema in Structuring a complex schema. Note that this should be used only when the entire string contains only JSON Pointer content, e.g.
/foo/bar. JSON Pointer URI fragments, e.g.
"relative-json-pointer":New in draft 7A relative JSON pointer.
"regex":New in draft 7A regular expression, which should be valid according to the ECMA 262 dialect.
Be careful, in practice, JSON schema validators are only required to accept the safe subset of regular expressions described elsewhere in this document.