Address validator block

The address validator block checks what customers type into address and contact fields. When a field breaks one of your rules, customers see your error message and can’t continue until they fix it. Common uses are blocking PO boxes, keeping fields short enough for shipping labels, and rejecting characters your carrier can’t print.

Only stores that installed Checkout Buddy before November 11, 2026 can create this block; other stores use the Address blocker function, which checks addresses when the customer submits. The block needs Shopify Plus, is available on the Free and Buddy plans, and shows in the Checkout Buddy (v1) app block.

Block or function?

Checkout Buddy has two ways to validate addresses. Both are under the Address blocker card in Create customization.

	Address validator block (this page)	Address blocker function
Needs the Checkout Editor	Yes	No
Fields it can check	Shipping, billing, contact phone, and email	Shipping address fields
Conditions	All block conditions	Address and weight conditions
Covers express checkouts that skip the address form	No	Yes
Plan	Free or Buddy	Deals & Rules or Buddy

Use the function when the rule must never be bypassed. Use the block when you need billing or email checks or richer conditions.

Set it up

1. On the Checkout rules tab, click Create customization, choose Address blocker, then Address validator, marked Checkout. Click Add rule under Address validation rules and pick a rule type.

2. Fill in the rule’s value, an Error message, and tick the Fields applied to. A rule with no fields ticked does nothing.

3. Add more rules if needed. Every failing rule shows its own error.

4. Add the block in the Checkout Editor, in its own Checkout Buddy (v1) app block with a Fixed block ID. It doesn’t show anything on the page, but it must be placed to work. Put it on the information or shipping step.

5. In the Checkout Editor, turn on Allow app to block checkout in the app block’s settings. Without this, no errors are shown and customers can continue.

Rule types

Rule	Error shows when	Value
Character limit	The field is longer than the limit	A number
Character minimum	The field is shorter than the minimum. Empty fields pass, so add Required too if needed.	A number
Excluded characters/words	The field contains any listed character or word, ignoring capitals	A comma-separated list, such as @, #, %, c/o
Value match	The field isn’t exactly one of the listed values. Capitals must match.	A comma-separated list. End an entry with * to match anything starting with it.
Custom regex	The field doesn’t match the regular expression	A JavaScript regular expression
Required	The field is empty	None
Exclude P.O. Box	The field looks like a PO box, for example “PO Box 12”, “P.O. 12”, or “Post office box 12”	None

Value match examples

M5J 0A7, M5J*, 12345*

• M5J 0A7 matches exactly “M5J 0A7”.
• M5J* matches anything starting with “M5J”.
• 12345* matches “12345”, “123456”, and “12345-6789”.

This is useful for limiting delivery to certain postal codes. Customers with any other value see the error.

Custom regex examples

To allow	Pattern
Latin letters, spaces, and hyphens	^[À-ÿA-Za-z \-]+$
Latin letters, numbers, spaces, and hyphens	^[À-ÿA-Za-z0-9 \-]+$
A US ZIP code	^\d{5}(-\d{4})?$

Test patterns at regex101.com with the JavaScript flavor.

Fields

• Shipping address: Address 1, Address 2, City, Zip/Post code, Phone (shipping address), Company, First name, Last name
• Billing address: Billing address 1, Billing address 2, Billing city, Billing zip/post code, Phone (billing address), Billing first name, Billing last name, Billing company
• Contact: Phone (contact), Email

Errors on shipping and contact fields show under the field. Errors on billing fields show at the top of checkout, since Shopify doesn’t let apps attach errors to billing fields.

Things to know

• Use Value match and Custom regex on fields customers always fill in, such as Zip/Post code or City. On optional fields like Address 2 or Company, these rules don’t work reliably when the field is left empty. (Address 1 is the exception: it’s skipped while empty.)
• Only one block shows per app block. Give the validator its own app block and Fixed block ID, or another block can take its spot and the rules won’t run. See which block shows.
• Error messages aren’t translated. Write them in your store’s main language, or create one block per market with each block’s Markets setting.
• Use conditions to apply your rules only sometimes, for example block PO boxes only when Shipping country includes United States.