CORS, an abbreviation for “Cross-Origin Resource Sharing,” fundamentally aims to ensure that data is distributed only to “trusted” users. However, this assurance is not server-side but rather on the client side. For instance, if CORS is enabled on a server, it sends additional response headers, allowing the client to verify whether the request is permitted from the current origin domain.

Modern browsers block access to data that is not considered “trusted” for the current origin domain. These are the CORS errors that often occur in the browser’s network tab. Using developer tools such as Postman, data can be retrieved from origins not deemed “trusted” because CORS validation is simply ignored. This can occasionally complicate the analysis of such issues.