CORS (Cross-Origin Resource Sharing) is a system, consisting of transmitting , that determines whether browsers block frontend JavaScript code from accessing responses for cross-origin requests.

The same-origin security policy forbids cross-origin access to resources. But CORS gives web servers the ability to say they want to opt into allowing cross-origin access to their resources.

CORS headers

• : Indicates whether the response can be shared.

• : Indicates whether or not the response to the request can be exposed when the credentials flag is true.

• : Used in response to a preflight request to indicate which HTTP headers can be used when making the actual request.

• : Specifies the method or methods allowed when accessing the resource in response to a preflight request.

• : Indicates which headers can be exposed as part of the response by listing their names.

• : Indicates how long the results of a preflight request can be cached.

• : Used when issuing a preflight request to let the server know which HTTP headers will be used when the actual request is made.

• : Used when issuing a preflight request to let the server know which HTTP method will be used when the actual request is made.

• : Indicates where a fetch originates from.

• : Specifies origins that are allowed to see values of attributes retrieved via features of the Resource Timing API, which would otherwise be reported as zero due to cross-origin restrictions.

See also

• Cross-Origin Resource Sharing (CORS)

• Cross-origin resource sharing on Wikipedia

• Fetch specification