USPS Web Tools (XML, deprecated)

USPS Web Tools is the pre-OAuth USPS API surface. Integrators issue HTTP GET or POST requests with an XML payload encoded into a query parameter (`API=<name>&XML=<payload>`), and authenticate using a UserID passed in the URL. There is no token, no rotation, and no account-scoped authorization beyond the UserID. The contract is XML-only and predates RFC 9457 problem details, so error responses are XML elements rather than structured problem objects. USPS has been migrating customers off Web Tools onto the modern REST USPS APIs at developer.usps.com. Web Tools still works for many operations at this page's last review, but it is the deprecated surface and integrators should not target it for greenfield work. Existing Web Tools integrations should plan a migration window with parallel running against the REST APIs, because the field shapes, error vocabularies, and account-identifier requirements differ between the two. This page exists primarily to redirect search traffic. Integrators searching for `USPS Web Tools` should land on a clear explanation of the deprecation and the replacement surface, not on a 404 or on outdated marketing copy. Treat any new Web Tools-only requirement as a sev-3 to investigate, on the assumption that the REST APIs already cover the operation under a different name.