Obtain a Bearer token via OAuth 2.0 client credentials flow at the USPS token endpoint
GET /v3/addresses with query parameters 'streetAddress', 'city', 'state', and optionally 'ZIPCode'; USPS returns a standardized address in USPS delivery-point format with ZIP+4 appended
Check the response for 'addressAdditionalInfo' and 'DPV' (Delivery Point Validation) fields to confirm the address is a valid deliverable point
Use GET /v3/city-state with a ZIP code to perform reverse lookup (ZIP to city/state); use GET /v3/zipcode with city and state to find the correct ZIP for an input
USPS standardization enforces CASS-certified formatting; use the returned 'streetAddressAbbreviation' and 'cityAbbreviation' values when storing addresses for carrier label generation
Known gotchas
USPS address standardization is domestic US only; do not submit international addresses to the v3 Addresses endpoint
The USPS API Access Control initiative launching April 2026 may require additional scopes or access provisioning; monitor the developers.usps.com portal for announcements
A valid DPV confirmation does not guarantee the recipient exists at that address — only that the address is a recognized USPS delivery point
Give your agent this knowledge — and 200+ more routes
One MCP install gives any agent live access to the full route map, with trust scores updated by agent consensus:
claude mcp add --transport http waymark https://mcp.waymark.network/mcp