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What is a postcode lookup API and how does it work?
A plain-English guide to what a postcode lookup API does, how it works, and where it fits in your product.
Guides
The short version
A postcode lookup API takes a UK postcode and returns the list of addresses at that postcode as structured data. Instead of asking a customer to type their full address, you let them enter a postcode and choose from the results.
How a request works
Your application sends the postcode and an API key to the provider over HTTPS. The API responds with JSON containing each matching address split into fields such as address line 1, line 2, town, and postcode. Your front end then displays the options for the user to select.
Where to use it
- Checkout — Speed up address entry and reduce abandonment.
- Onboarding — Capture clean customer addresses from the first form.
- Delivery — Feed structured, deliverable addresses into fulfilment.
What to look for
Prioritise response speed, data freshness, comprehensive coverage, and a simple, well-documented API. These are the factors that affect day-to-day experience and engineering effort.