Validation

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

How to Verify an Address: Format, Existence, OccupantHow to verify an address in three levels: format check, match against postal data, proof that someone lives there. Free tools and what each one misses.
Postcode Regex: Tested Patterns for UK, US, CA, DE, NL, IEPostcode regex patterns for six countries, tested, with a normalising step. Plus the anchoring bug in the UK government regex that accepts garbage.
Address Autocomplete in Checkout: Setup and PitfallsAddress autocomplete in checkout cuts typing errors, but drops flat numbers and misses parcel lockers. Setup with autocomplete tokens, costs and fallbacks.
Address Validation API: How to Choose and What to TestAn address validation API returns a corrected address and a verdict on deliverability. Provider types, Google's 2026 prices, and a test plan with your data.