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HTTP Header
Access-Control-Request-Headers
CORSLists which request headers will be used in the actual cross-origin request during a preflight request.
HTTP header reference, syntax, examples, and developer usage.
What is the Access-Control-Request-Headers header?
The Access-Control-Request-Headers HTTP header is used to transmit metadata between a client and server as part of HTTP requests or responses.
HTTP headers define how content should be interpreted, cached, authenticated, secured, or processed by browsers and APIs.
Direction
This header may appear in both HTTP requests and responses.
Syntax
Access-Control-Request-Headers: header1, header2
Example
Access-Control-Request-Headers: authorization, content-type
Common use cases
- CORS preflight requests
- Declaring custom headers before actual request
- Frontend API debugging
Common mistakes
- Using the header in the wrong request or response context
- Sending invalid header values
- Incorrect header syntax
- Assuming the header automatically changes server behaviour