Laminas\Validator\IsJsonString allows you to validate whether a given value is a string that will be successfully decoded by json_decode.

Basic Usage

$validator = new Laminas\Validator\IsJsonString();
$input = '{"some":"json"}';

if ($validator->isValid($input)) {
    // $input can be successfully decoded
} else {
    // $input is not a valid JSON string

Restricting Acceptable JSON Types

json_decode accepts numeric strings representing integers and floating point numbers, booleans, arrays and objects. You can restrict what is considered valid input using the allow option of the validator.

use Laminas\Validator\IsJsonString;

$validator = new IsJsonString([
    'allow' => IsJsonString::ALLOW_ALL ^ IsJsonString::ALLOW_BOOL,

$validator->isValid('true'); // false

The allow option is a bit mask of the ALLOW_* constants in IsJsonString:

  • IsJsonString::ALLOW_INT - Accept integer such as 1
  • IsJsonString::ALLOW_FLOAT - Accept floating-point value such as 1.234
  • IsJsonString::ALLOW_BOOL - Accept true and false
  • IsJsonString::ALLOW_ARRAY - Accept JSON arrays such as ["One", "Two"]
  • IsJsonString::ALLOW_OBJECT - Accept JSON objects such as {"Some":"Object"}
  • IsJsonString::ALLOW_ALL - A convenience constant allowing all of the above (Also the default).

The allow option also has a companion setter method setAllow. For example, to only accept arrays and objects:

use Laminas\Validator\IsJsonString;

$validator = new IsJsonString();
$validator->setAllow(IsJsonString::ALLOW_ARRAY | IsJsonString::ALLOW_OBJECT);
$validator->isValid('1.234'); // false

Restricting Max Object or Array Nesting Level

If you wish to restrict the nesting level of arrays and objects that are considered valid, the validator accepts a maxDepth option. The default value of this option is 512 - the same default value as json_decode.

$validator = new Laminas\Validator\IsJsonString(['maxDepth' => 2]);
$validator->isValid('{"nested": {"object: "here"}}'); // false

Again, the max nesting level allowed has a companion setter method:

$validator = new Laminas\Validator\IsJsonString();