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A regular expression (regex) is a pattern that describes what a value should look like. Use this rule when a field must follow an exact format, like a 6-digit postcode or a 10-digit mobile number.

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How it works

You add one or more fields. For each field you set a pattern and choose when to block:
  • Matched: block checkout when the value matches the pattern. Use this for things you don’t want, such as numbers in a name.
  • Unmatched: block checkout when the value doesn’t match the pattern. Use this for a format the value must follow, such as a postcode.
Empty fields are not checked. Matching ignores upper and lower case.
Matched blocks John2 because it contains a number. Unmatched blocks 11001 because it isn't a 6-digit postcode.

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Set up the rule

1

Select the fields

Under Add validation to these fields, click the box and tick the fields to check. Each field gets its own card.
2

Enter a pattern

In the field’s card, type a pattern in Custom Regular Expression, or click the presets button and choose one of the ready-made patterns. Choosing a preset also sets When for you.
3

Choose when to block

Under When, choose Matched or Unmatched.
4

Choose shipping or billing

For address fields, tick Shipping address, Billing address or both.
5

Write the message

Under Message to display in the field’s card, write what the customer sees. English is required for each field.

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Fields you can check

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Ready-made patterns

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More example patterns

Not sure how to write a pattern? Describe what you need to an AI assistant, or contact us with your example and we’ll help you write it.
Test every pattern with the Testing status first. A pattern that is too strict can block real customers. If a pattern isn’t valid, the app skips that field instead of blocking checkout.

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Other settings

This rule also has the Countries, Rule status and Checkout behavior settings described in Common rule settings.