What CORS is
CORS, which stands for cross-origin resource sharing, is a mechanism that allows a server to indicate which other origins are permitted to access its resources from a web browser. Normally the same-origin policy restricts cross-origin access, but there are legitimate reasons for sites to share resources across origins. CORS provides a controlled, standardized way to allow this when it is intended.
Relaxing the same-origin policy safely
The same-origin policy blocks cross-origin access by default to protect users. However, modern web applications often need content or data from different origins to cooperate. CORS lets servers selectively relax this restriction by declaring which outside origins may access their resources. This keeps the secure default in place while permitting deliberate, approved cross-origin sharing.
How CORS works
With CORS, when a web page tries to access a resource from a different origin, the browser checks whether the server has indicated that such access is allowed. The server communicates its permissions, and the browser enforces them. If the server permits the requesting origin, the access proceeds; if not, the browser blocks it. This puts the server in control of who may use its resources.
The browser's role
CORS depends on the browser to enforce the rules. The browser mediates cross-origin requests, consulting the server's stated permissions and allowing or denying access accordingly. Because the enforcement happens in the browser, the protections apply consistently. This cooperation between server-declared permissions and browser enforcement is what makes CORS a safe way to manage cross-origin access.
Why CORS is useful
CORS is useful because it enables the legitimate sharing of resources between origins without simply abandoning the protections of the same-origin policy. Servers can open up specific resources to specific origins as needed, supporting modern web applications that draw on multiple sources. This balance of flexibility and control is why CORS is an important part of the web platform.
Why it matters
CORS is an important web security mechanism to understand. Knowing what it is - a controlled way for servers to allow cross-origin access to their resources - clarifies how the web balances security with the need for sites to cooperate. For anyone interested in web security, it is a valuable concept to understand.
Related on Skillo
See also: What is the same-origin policy? Explained, What is an API? Explained simply.
Sources
Published date reflects the original event date (2026-06-02). This article is original Skillo editorial written from the sources above; facts were verified in September 2026.
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