Address Validation for Real Estate and Property Data

An address validation API for real estate and property data checks US property addresses against postal data and standardizes the ones it matches into one form: street, unit, city, state, ZIP+4 and county. You then use that form to find listings, tax records and CRM entries that may be the same property. It does not tell you who owns the property or what it is worth; property data APIs such as ATTOM and BatchData sell that.

Why property records need one address form

A listing feed may say "525 South Winchester Boulevard". A tax record may say "525 S Winchester Blvd". A plain text match treats them as two properties. In our test the long form came back as "525 S Winchester Blvd, San Jose, CA 95128-2537", so both records now share the same street line and show up as a candidate match.

Four parts of the address do most of the work when you match records:

• Street line. Abbreviations, directions and suffixes written one way ("S", "Blvd").
• Unit. Returned as its own fields (unit type and unit number). In our test, "#900" came back as unit type "STE" and unit number "900".
• ZIP+4. The four digits after the ZIP Code. In our test, a suite and its building got different ZIP+4 codes (see below).
• County. Useful when you join to county-level records. Verification returns the county name, for example "Santa Clara". Geocoding returns "Santa Clara County" plus a numeric county code, "06085". Pick one form before you join.

Live test: a landmark and an office building

We sent three addresses to the sthan.io verification API on October 16, 2026: a landmark in San Jose with no units, one suite in a San Francisco office building, and the same building with no suite. Each answered in under 2 seconds.

Four things stand out. The San Jose input had no ZIP Code; the response filled in 95128-2537 and marked both the ZIP Code and the ZIP+4 as inferred. The "#900" came back split into unit type "STE" and unit number "900". The building without a suite came back ConfirmedPrimaryOnly, which sthan.io's documentation defines as "primary OK but secondary unit missing or invalid", with a different ZIP+4 (1307) from the suite (1337). And that building record had record type S, while the suite had H, so the record type alone does not tell you a building has units.

Find duplicates on the standardized address

The building result above is the trap. If one record has the suite and another does not, they get different ZIP+4 codes, so a key built on ZIP+4 splits them, and a key built on street and 5-digit ZIP alone lumps every suite in the building together. A shared address also does not prove that two listings, sales or parcel records are the same property.

Our suggested workflow: use the standardized street, unit and ZIP to find candidate matches, then confirm the property or parcel identifier and the record type before you merge.

Coordinates do not settle it either. In our geocoding test below, the suite and the building came back as two points 39.2 meters apart, so do not merge records on latitude and longitude.

For a property file in a spreadsheet, the same logic applies: verify each row once, store the standardized fields next to the original, and look for candidate duplicates on the stored fields. sthan.io's Address Cleaner takes an Excel, .csv or .tsv file of up to 100,000 rows and gives back your original columns plus the cleaned address, ZIP+4, county and a status for every row. It costs $1.20 per 1,000 rows found in postal records; rows that need review or are not found are free, and your first 100 rows each day are free.

Geocode for maps

Maps and radius searches need coordinates, which come from a geocoding API, a separate product from verification. sthan.io's forward geocoding endpoint is /Geocoding/USA/Forward/{address} and the reverse endpoint is /Geocoding/USA/Reverse/{lat}/{lon}. Here is what they returned on October 16, 2026:

The reverse lookup on the San Jose point came back to the same address. All four answers carried a county, written with the word "County" and a numeric code, which differs from the verification response. Forward and reverse geocoding are included together in the same plan: 3,000 free requests a month (up to 100 a day), then from $5 a month for 10,000.

A geocoder tells you where an address sits on the map. It is not a deliverability check, so run verification first if you also need the standardized postal address.

Address verification and property data APIs answer different questions

sthan.io's address verification and property data APIs such as ATTOM and BatchData are different products. They answer different questions, so their prices are not comparable.

The two work together: standardize the address first, then look it up in a property data source.

Sources

All read October 16, 2026: live sthan.io API calls to /v2/address-verification/usa/ (three addresses above), /Geocoding/USA/Forward/ (three addresses above) and /Geocoding/USA/Reverse/ (the San Jose point); sthan.io/docs (deliverableStatus and recordType definitions, geocoding paths, free-tier limits); sthan.io/products/address-verification-usa; sthan.io/products/geocoding-usa; sthan.io/products/reverse-geocoding-usa; sthan.io/address-cleaner; api.developer.attomdata.com/docs; attomdata.com/data/property-data/; batchdata.io. Prices change; check the vendor page before you buy.