POST to /v1/addresses with the address fields (name, street1, city, state, zip, country in ISO 3166-1 alpha-2 format) and 'validate': true
Inspect the response 'validation_results' object: 'is_valid' indicates whether the address is deliverable; 'messages' contains an array of specific errors or warnings
For US addresses, Shippo returns USPS standardized output including ZIP+4; for international addresses, confidence levels vary by country coverage
If 'is_valid' is false, surface the 'messages' text to the user or pass to an address correction flow before attempting label creation
Validate addresses at order capture time, not only at label generation time, to catch problems before fulfillment
Known gotchas
International address validation coverage varies significantly by country; Shippo may return 'is_valid': true for addresses it cannot fully validate — treat international validation as a best-effort check rather than a guarantee
Shippo address validation is a separate API call from label creation; the validate flag on the address object does not automatically prevent label purchase for an invalid address
A validated address can still fail at the carrier level due to carrier-specific formatting requirements (e.g., required state codes, postal code formats); always review carrier-specific address guidelines for key destination markets
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