The answer
PUT, DELETE, PATCH, or any request with application/json Content-Type or custom headers (Authorization, X-Custom). These trigger a preflight OPTIONS request before the actual request.
CORS: Simple vs Non-Simple Requests
What is a non-simple CORS request?
More FAQs in CORS: Simple vs Non-Simple Requests
GET, POST, or HEAD with a safe Content-Type (form-urlencoded, multipart, text/plain) and no custom headers. The browser sends it directly without a preflight and checks the response headers.
Yes. application/json is not a 'safe' Content-Type. The browser sends an OPTIONS preflight first. Only form-urlencoded, multipart/form-data, and text/plain are safe.
Yes. Authorization is a custom header (not in the CORS-safe list). Any request with an Authorization header triggers a preflight, even a GET.
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