Edit this page on Github

The Meta Box plugin has built-in validation module for all fields. You can use validation to make a field required, check password length, check phone number format, etc. The validation is done on the client side.

There are 2 ways of doing validation: via input attributes (mostly for basic validation) and via jQuery validation plugin (for more advanced validation). They’re both bundled in Meta Box and you can choose which one fits your needs.

Validation with input attributes

Meta Box supports custom attributes for all input fields. You can use these attributes to add validation rules like this:

// This is an array settings of a text field.
    'type' => 'text',
    'id'   => 'phone',
    'name' => 'Phone number',
    // Attributes for validation.
    'required' => true,       // Make the field required.
    'pattern'  => '[0-9]{9}', // Must have 9 digits

These are the available attributes that you can use for validation:

Attribute Description
max Maximum value
maxlength Maximum number of characters
min Minimum value
minlength Minimum number of characters
pattern Match a regular expression
required Required
step Match the step increment
type Match the input type

Validation with jQuery validation plugin

For more advanced validation, including new rules and custom error messages, you might want to use the validation module, powered by the popular jQuery validation plugin. It comes bundled with a useful set of validation methods and an API to write your own methods. All methods come with default error messages in English and translations into 37 other languages.

To use it, you need to add a key validation to the meta box settings. This key has a parameter rules for validation rules and messages for error messages.

// This is a part of the meta box settings
'validation' => [
    'rules'  => [
        'field_id' => [
            'required'  => true,
            'minlength' => 7,
            // More rules here
        // Rules for other fields
    'messages' => [
        'field_id' => [
            'required'  => 'Password is required',
            'minlength' => 'Password must be at least 7 characters',

These are available validation rules that you can use:

Name Description
required Makes the element required.
minlength Makes the element require a given minimum length.
maxlength Makes the element require a given maxmimum length.
rangelength Makes the element require a given value range. Array.
min Makes the element require a given minimum.
max Makes the element require a given maximum.
range Makes the element require a given value range. Array.
email Makes the element require a valid email
url Makes the element require a valid url
date Makes the element require a date.
dateISO Makes the element require an ISO date.
number Makes the element require a decimal number.
digits Makes the element require digits only.
creditcard Makes the element require a credit card number.
equalTo Requires the element to be the same as another one. Value must be the ID of another field.
extension Makes the element require certain file extensions. For file, image fields only.
accept Makes a file upload accept only specified mime-types. For file, image fields only.
phoneUS Validate for valid US phone number.
remote Requests a resource to check the element for validity. Value can be URL of the resource to request for server side validation (string) or options to fully customize the request, see jQuery.ajax. The server side resource is called via jQuery.ajax and gets a key/value pair corresponding to the name of the validated element and its value as a GET parameter. The response is evaluated as JSON and must be true for valid elements, and can be any false, undefined or null for invalid elements, using the default message; or a string, eg. “That name is already taken, try peter123 instead” to display as the error message.

For more details about validation rules, please read the jQuery validation documentation.


The jQuery validation library actually uses input name, not input ID. In most cases, field ID is the same as field name. But for some cases such as field is a checkbox list or is a taxonomy with field_type is checkbox_list, e.g. where field has multiple inputs, then all those inputs don’t have IDs.

In this case, you need to use input name for the rules. For example, if you use a taxonomy field with field_type is checkbox_list, you should set validation rules as follows:

'validation' => [
    'rules'  => [
        'my_taxonomy[]' => [
            'required'  => true,
    'messages' => [
        'my_taxonomy[]' => [
            'required'  => 'You must select a tag to proceed',

Edit this page on Github