# Validation – AddressValid

> Checkout forms, autocomplete, APIs and the errors they catch or miss.

- [How to Verify an Address: Format, Existence, Occupant](https://address-valid.com/validation/verify-an-address/): To verify an address, check it at three levels. First the format: postcode pattern, house number, line order. Then existence: match it against postal data, for example with the USPS ZIP Code lookup or an address validation API. Finally the occupant, if it matters, with a document or a letter that must be answered.
- [Postcode Regex: Tested Patterns for UK, US, CA, DE, NL, IE](https://address-valid.com/validation/postcode-regex/): A postcode regex should check one country's pattern on input that has been trimmed, uppercased and given its standard spacing. For the UK that means six outward-code shapes plus GIR 0AA; for the US five digits with an optional hyphen and four more. A regex confirms the shape only, never that the postcode exists.
- [Address Autocomplete in Checkout: Setup and Pitfalls](https://address-valid.com/validation/address-autocomplete-checkout/): Address autocomplete in checkout suggests complete addresses as the customer types and fills the form fields on selection. Set the standard autocomplete tokens so browser autofill works, add a suggestion service on the first address line, keep the unit field visible, and always allow manual entry when the address is not in the list.
- [Address Validation API: How to Choose and What to Test](https://address-valid.com/validation/address-validation-api/): An address validation API takes an address, matches it against postal or commercial reference data and returns a standardized version with a verdict: how precisely it matched, which parts were corrected or inferred, and whether the address looks deliverable. Choose by coverage of your countries, unit-level accuracy, price at your volume and data handling terms.

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