Use the connected request workflow
Compose or parse the request, convert it to the representation your stack needs, inspect captured traffic and headers, then diagnose cache/CORS/security policy before testing the real endpoint.
Local analysis is not remote verification
Unless a tool explicitly has a direct-fetch action, these HTTP tools do not contact endpoints. Browser fetch cannot bypass CORS, and generated policy text does not prove how a deployed server, browser, proxy or CDN will behave.