Subscriptions

GraphQL subscriptions are where CORS advice usually gets sloppy. A lot of teams learn CORS from regular fetch() requests, then bolt on subscriptions and assume the same rules apply. They do not. The transport matters: HTTP GraphQL queries/mutations: normal CORS rules WebSocket subscriptions: not governed by browser CORS in the same way SSE subscriptions: back to normal HTTP-origin behavior Multipart/deferred streaming over HTTP: also normal CORS behavior If you only remember one thing, remember this: GraphQL subscriptions over WebSocket do not use CORS the way fetch() does, but origin validation still matters. ...