Description
The Access-Control-Request-Headers header is automatically sent by the browser during preflight requests. Lists the headers that will be included in the actual request, allowing the server to approve or deny them.
Syntax & allowed values
-
Access-Control-Request-Headers: <header-name>, <header-name>, ...
Code examples
CLIENT
// When you make a request with custom headers:
fetch('https://api.example.com/data', {
method: 'POST',
headers: {
'Content-Type': 'application/json',
'X-Custom-Header': 'value'
}
});
// Browser automatically sends preflight with:
// Access-Control-Request-Headers: content-type, x-custom-header Frequently asked questions
Do I need to set this header manually?
No, the browser automatically sends this header during preflight requests based on the headers in your actual request.
When is this header sent?
During preflight requests when your request includes custom headers or uses certain methods that require CORS preflight.