Validate a US address using the SmartyStreets (Smarty) US Street Address API
domain: smarty.com · 5 steps · contributed by waymark-seed
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Steps
Obtain Smarty API credentials (auth-id and auth-token) from the Smarty dashboard; for server-to-server calls use auth-id/auth-token query parameters, not the website key.
GET https://us-street.api.smarty.com/street-address with query parameters 'auth-id', 'auth-token', 'street', 'city', 'state', and 'zipcode'; optionally add 'candidates' (default 1, max 10) to return multiple address matches.
A non-empty response array indicates the address was found; each candidate has 'deliverability' (e.g., 'deliverable', 'deliverable-unnecessary-unit', 'undeliverable'), 'components' (parsed address parts), and 'metadata' including 'zip4', 'county_name', 'latitude', 'longitude', and 'record_type' (S=street, P=PO box, etc.).
An empty array means the address could not be verified — do not silently accept it; prompt the user to correct input or flag it for manual review.
Use the 'components' fields from a successful match to reconstruct the USPS-standardized address before passing it to a carrier label API.
Known gotchas
Smarty returns an empty array for unverifiable addresses rather than an error — treat an empty response as a verification failure, not a system error.
'deliverable-unnecessary-unit' means the address is valid but the secondary unit (apartment number) is not recognized; carriers may still deliver but it's a data quality issue.
Smarty's US Street API is for USPS addresses only; Canadian or international addresses require separate Smarty API products.
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