validate.rst

Schema Validation

jsonschema

The Basics

The simplest way to validate an instance under a given schema is to use the validate function.

validate

The Validator Protocol

jsonschema defines a protocol that all validator classes should adhere to.

jsonschema.protocols.Validator

All of the versioned validators <versioned-validators> that are included with jsonschema adhere to the protocol, and implementers of validator classes that extend or complement the ones included should adhere to it as well. For more information see creating-validators.

Type Checking

To handle JSON Schema's type property, a Validator uses an associated TypeChecker. The type checker provides an immutable mapping between names of types and functions that can test if an instance is of that type. The defaults are suitable for most users - each of the versioned validators <versioned-validators> that are included with jsonschema have a TypeChecker that can correctly handle their respective versions.

validating-types

For an example of providing a custom type check.

TypeChecker

jsonschema.exceptions.UndefinedTypeCheck

Raised when trying to remove a type check that is not known to this TypeChecker, or when calling jsonschema.TypeChecker.is_type directly.

Validating With Additional Types

Occasionally it can be useful to provide additional or alternate types when validating the JSON Schema's type property.

jsonschema tries to strike a balance between performance in the common case and generality. For instance, JSON Schema defines a number type, which can be validated with a schema such as {"type" : "number"}. By default, this will accept instances of Python numbers.Number. This includes in particular ints and floats, along with decimal.Decimal objects, complex numbers etc. For integer and object, however, rather than checking for numbers.Integral and collections.abc.Mapping, jsonschema simply checks for int and dict, since the more general instance checks can introduce significant slowdown, especially given how common validating these types are.

If you do want the generality, or just want to add a few specific additional types as being acceptable for a validator object, then you should update an existing TypeChecker or create a new one. You may then create a new Validator via jsonschema.validators.extend.

class MyInteger(object):
    pass

def is_my_int(checker, instance):
    return (
        Draft3Validator.TYPE_CHECKER.is_type(instance, "number") or
        isinstance(instance, MyInteger)
    )

type_checker = Draft3Validator.TYPE_CHECKER.redefine("number", is_my_int)

CustomValidator = extend(Draft3Validator, type_checker=type_checker)
validator = CustomValidator(schema={"type" : "number"})

jsonschema.exceptions.UnknownType

Versioned Validators

jsonschema ships with validator classes for various versions of the JSON Schema specification. For details on the methods and attributes that each validator class provides see the Validator protocol, which each included validator class implements.

Draft202012Validator

Draft201909Validator

Draft7Validator

Draft6Validator

Draft4Validator

Draft3Validator

For example, if you wanted to validate a schema you created against the Draft 7 meta-schema, you could use:

from jsonschema import Draft7Validator

schema = {
    "$schema": "http://json-schema.org/draft-07/schema#",

    "type": "object",
    "properties": {
        "name": {"type": "string"},
        "email": {"type": "string"},
    },
    "required": ["email"]
}
Draft7Validator.check_schema(schema)

Validating Formats

JSON Schema defines the format property which can be used to check if primitive types (strings, numbers, booleans) conform to well-defined formats. By default, no validation is enforced, but optionally, validation can be enabled by hooking in a format-checking object into an Validator.

>>> validate("127.0.0.1", {"format" : "ipv4"}) >>> validate( ... instance="-12", ... schema={"format" : "ipv4"}, ... format_checker=draft7_format_checker, ... ) Traceback (most recent call last): ... ValidationError: "-12" is not a "ipv4"

FormatChecker

checkers

A mapping of currently known formats to tuple of functions that validate them and errors that should be caught. New checkers can be added and removed either per-instance or globally for all checkers using the FormatChecker.checks or FormatChecker.cls_checks decorators respectively.

cls_checks(format, raises=())

Register a decorated function as globally validating a new format.

Any instance created after this function is called will pick up the supplied checker.

argument str format

the format that the decorated function will check

argument Exception raises

the exception(s) raised by the decorated function when an invalid instance is found. The exception object will be accessible as the jsonschema.exceptions.ValidationError.cause attribute of the resulting validation error.

FormatError

There are a number of default checkers that FormatCheckers know how to validate. Their names can be viewed by inspecting the FormatChecker.checkers attribute. Certain checkers will only be available if an appropriate package is available for use. The easiest way to ensure you have what is needed is to install jsonschema using the format or format_nongpl collection of optional dependencies -- e.g.

$ pip install jsonschema[format]

which will install all of the below dependencies for all formats.

Or if you want to install MIT-license compatible dependencies only:

$ pip install jsonschema[format_nongpl]

The non-GPL extra is intended to not install any direct dependencies that are GPL (but that of course end-users should do their own verification). At the moment, it supports all the available checkers except for iri and iri-reference.

The more specific list of available checkers, along with their requirement (if any,) are listed below.

Note

If the following packages are not installed when using a checker that requires it, validation will succeed without throwing an error, as specified by the JSON Schema specification.

Checker	Notes
color date	requires webcolors
date-time	requires rfc3339-validator
duration email	requires isoduration
hostname	requires fqdn
idn-hostname ipv4	requires idna
ipv6	OS must have socket.inet_pton function
iri	requires rfc3987
iri-reference	requires rfc3987
json-pointer regex	requires jsonpointer
relative-json-pointer	requires jsonpointer
time	requires rfc3339-validator
uri	requires rfc3987 or rfc3986-validator
uri-reference	requires rfc3987 or rfc3986-validator
uri-template	requires uri-template

Note

Since in most cases "validating" an email address is an attempt instead to confirm that mail sent to it will deliver to a recipient, and that that recipient is the correct one the email is intended for, and since many valid email addresses are in many places incorrectly rejected, and many invalid email addresses are in many places incorrectly accepted, the email format validator only provides a sanity check, not full rfc5322 validation.

The same applies to the idn-email format.