Postcodes.io

Postcodes.io

Open-source UK postcode and geolocation API powered by Ordnance Survey and ONS data. Read access does not use a vendor credential flow.

Data Model

• Postcode — Full UK postcode (e.g. "SW1A 1AA"). Returns coordinates, admin geography, parliamentary constituencies, NHS regions, and statistical geography codes.
• Outcode — First part of a postcode (e.g. "SW1A"). Returns averaged coordinates and lists of associated admin districts, parishes, and wards.
• Quality — Integer 1-9 indicating positional quality (1 = within building, 9 = no coordinates).

Key Fields in Postcode Results

• admin_district — Local authority (e.g. "Westminster")
• parliamentary_constituency — Current constituency name
• region — English region (null for Scotland, Wales, NI)
• lsoa / msoa — Lower/Middle Super Output Areas (statistical geography)
• ccg / icb — NHS Clinical Commissioning Group / Integrated Care Board
• pfa — Police Force Area

Gotchas

• Spaces in postcodes: The API handles both "SW1A 1AA" and "SW1A1AA" — spaces are optional.
• Terminated postcodes: Some postcodes are no longer in use. The lookup endpoint returns null for these; use the terminated postcodes endpoint if needed.
• Bulk limit: Bulk lookup accepts up to 100 postcodes per request.
• Reverse geocode: Returns up to 10 nearest postcodes within a configurable radius (default 100m, max 2000m).
• Nearest: Returns postcodes near a given postcode within a configurable radius.