Access-Control-Allow-Origin
Response headers
Names which origins may read this response — the heart of CORS.
| On the wire | Access-Control-Allow-Origin: … |
|---|---|
| Category | Response headers |
Headers the server attaches when it answers.
How to read this
- The first digit of a status code carries the meaning: 4 means the request, 5 means the server.
- 404 means "not there"; 403 means "there, but not for you". Swapping them makes debugging slower.
- Header names are case-insensitive — Content-Type and content-type are the same header.
- Caching and CORS problems usually come down to one header line, visible in the browser’s network tab.
Frequently asked questions
Q. What does HTTP Access-Control-Allow-Origin mean?
Names which origins may read this response — the heart of CORS.
Q. What does Access-Control-Allow-Origin look like on the wire?
It travels as Access-Control-Allow-Origin: …
Q. Where does Access-Control-Allow-Origin appear?
In response headers.
Q. What group does Access-Control-Allow-Origin belong to?
The response headers group; the rest of that group is listed further down.