A (coercive) JSON Schema v4 Validator for PHP

v1.0.1 2014-10-07 13:36 UTC

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Last update: 2021-09-10 22:36:28 UTC


A (coercive) JSON Schema v4 Validator for PHP

jsv4-php is a data validator, using version 4 JSON Schemas.

Just include jsv4.php from your code, and use the static methods on the Jsv4 class it defines.


Jsv4::validate($data, $schema)

This usage returns an object of the following shape.

    "valid": true/false,
    "errors": [

The values in the errors array are similar to those for tv4 (a similar project):

    "code": 0,
    "message": "Invalid type: string",
    "dataPath": "/intKey",
    "schemaKey": "/properties/intKey/type"

The code property corresponds to a constant corresponding to the nature of the validation error, e.g. JSV4_INVALID_TYPE. The names of these constants (and their values) match up exactly with the constants from tv4.

Jsv4::isValid($data, $schema)

If you just want to know the validation status, and don't care what the errors actually are, then this is a more concise way of getting it.

It returns a boolean indicating whether the data correctly followed the schema.

Jsv4::coerce($data, $schema)

Sometimes, the data is not quite the correct shape - but it could be made the correct shape by simple modifications.

If you call Jsv4::coerce($data, $schema), then it will attempt to change the data.

If it is successful, then a modified version of the data can be found in $result->value.

It's not psychic - in fact, it's quite limited. What it currently does is:

Type-coercion for scalar types

Perhaps you are using data from $_GET, so everything's a string, but the schema says certain values should be integers or booleans.

Jsv4::coerce() will attempt to convert strings to numbers/booleans only where the schema says, leaving other numerically-value strings as strings.

Missing properties

Perhaps the API needs a complete object (described using "required" in the schema), but only a partial one was supplied.

Jsv4::coerce() will attempt to insert appropriate values for the missing properties, using a default (if it is defined in a nearby "properties" entry) or by creating a value if it knows the type.

The SchemaStore class

This class represents a collection of schemas. You include it from schema-store.php, and use it like this:

$store = new SchemaStore();
$store->add($url, $schema);
$retrieved = $store->get($url);

It can handle:

  • Fragments in URLs, using both JSON Pointer fragments and identification using "id"
  • Converts URIs in "id" and "$ref" to absolute (where possible)
  • Resolves "$ref"s, splicing the resulting value into the schema
  • Converts associative PHP arrays to objects - you can express your schema natively, but what you retrieve from the store is always an object.
  • Adds sub-schemas according to their "id" - by default, this only happens if "id" is a sub-path of the current schema URL.

If the schemas being added are "trusted", then an extra argument can be supplied: $store->add($url, $schema, TRUE). In that case, the value of "id" is always believed for all sub-schemas.

A list of "missing" schemas (unresolved "$ref"s) can be retrieved used $store->missing().

This class does not depend on jsv4.php at all - it just deals with raw schema objects. As such, it could (hopefully) be used with other validators with minimal fuss.


The tests can be run using test.php (from the command-line or via the web).


This code is released under a do-anything-you-like "public domain" license (see LICENSE.txt).

It is also released under an MIT-style license (see LICENSE-MIT.txt) because there is sometimes benefit in having a recognised open-source license.