Your shop ships from one depot and you want to know which orders fall outside a delivery radius, without paying for a mapping API or loading a postcode database. A UK postcode distance endpoint does it in one call per order.
The call
curl "https://uk-postcodekit-postcode-lookup-nearest-distance.p.rapidapi.com/distance?from=SW1A%201AA&to=M1%201AE" \ -H "X-RapidAPI-Key: YOUR_KEY" \ -H "X-RapidAPI-Host: uk-postcodekit-postcode-lookup-nearest-distance.p.rapidapi.com" Response:
{"distance_km":261.906,"distance_miles":162.741,"from":"SW1A 1AA","note":"Straight-line (great-circle) distance","to":"M1 1AE"} It is a straight-line distance, so treat it as a quick radius filter, not a driving distance.
The script
import os,requests,sys BASE=os.environ.get("BASE","https://uk-postcodekit-postcode-lookup-nearest-distance.p.rapidapi.com") H={"X-RapidAPI-Key":os.environ.get("RAPIDAPI_KEY","YOUR_KEY"),"X-RapidAPI-Host":"uk-postcodekit-postcode-lookup-nearest-distance.p.rapidapi.com"} def dist(a,b): r=requests.get(f"{BASE}/distance",headers=H,params={"from":a,"to":b},timeout=15);r.raise_for_status();return r.json()["distance_miles"] depot="M1 1AE" for pc in sys.argv[1:]: print(f"{pc:10} {dist(depot,pc):7.1f} miles from depot") Running it for three customer postcodes:
SW1A 1AA 162.7 miles from depot LS1 1UR 35.6 miles from depot EH1 1YZ 174.7 miles from depot Wiring it in
Wrap dist() in your checkout: reject or surcharge anything over your radius. Use /validate?postcode=... first to catch typos, and /lookup?postcode=... to get the district, ward, latitude and longitude for the order.
Doing it locally
You can download the ONS postcode directory (millions of rows), index it and write the haversine yourself. That is fine at scale, but for a small shop the API is a few lines and no data refresh to maintain.
Limits
The free plan is enough to try this on real orders; paid plans raise the monthly quota. Data is Open Government Licence v3.0 (OS / Royal Mail attribution is returned in /lookup).
