Validation for zip code field on checkout page in magento 2

To add validation on the zip field we should overwirte Magento_Checkout/layout/checkout_index_index.xml and add this code :

   <item name="validation" xsi:type="array">
        <item name="validate-zip-us" xsi:type="string">true</item>
    </item>

Like this

<item name="postcode" xsi:type="array">
    <item name="sortOrder" xsi:type="string">75</item>
        <!-- post-code field has custom UI component -->
    <item name="component" xsi:type="string">Magento_Ui/js/form/element/post-code</item>
    <item name="validation" xsi:type="array">
      <item name="required-entry" xsi:type="string">true</item>
      <item name="validate-zip-us" xsi:type="string">true</item>
    </item>
</item>

zip-range for example is a already defined rule in rules.js.

We can overwrite this rule or we can create another rule according to our needs in this location:Theme\Theme\Magento_Ui\web\js\lib\validation\rules.js >