The HTTP Status Code 103 is used to return some response headers before final HTTP message.
Frequently Asked Questions
What is HTTP status code 103?
HTTP 103 Early Hints is an informational status code (in the 1xx class) that a server sends before it has finished preparing the final response. It allows the server to return preliminary response headers — particularly Link headers — so the client can start preloading or preconnecting to resources it will likely need. The final response (such as a 200 OK) follows once the server is ready.
When does a server send a 103 response?
A server sends a 103 response when it knows which resources the final page will need but hasn't finished generating the full response yet — for example, while querying a database or rendering a template. By sending early hints in that gap, the server lets the browser begin fetching stylesheets, fonts, or scripts, or preconnect to CDN origins, before the main response arrives.
What is the difference between HTTP 103 and a 200 response?
A 200 OK is the final, complete response that contains the requested content. A 103 Early Hints response is a provisional, informational message sent before the final response — it carries only headers (primarily Link) and no response body. The browser processes the hints speculatively while waiting for the 200, which ultimately supersedes the 103.
How does HTTP 103 differ from HTTP 100 Continue?
Both are 1xx informational codes, but they serve different purposes. HTTP 100 Continue tells the client it can proceed with sending a request body (used when a client sends an Expect: 100-continue header). HTTP 103 Early Hints is server-initiated and carries resource hints about the upcoming response, allowing the browser to preload assets rather than signaling anything about the request itself.
Does HTTP 103 require HTTP/2?
HTTP 103 Early Hints is recommended for use over HTTP/2 or later. HTTP/1.1 clients can mishandle informational responses, which is why RFC 8297 advises servers to only send 103 responses over HTTP/2+ unless the client's behavior is known. Most browsers enforce this and will only process early hints delivered over HTTP/2 or HTTP/3.
Can a server send multiple 103 responses?
Yes, a server may send more than one 103 response — for instance, across a redirect chain. However, browsers only process the first early hints response they receive. If the request results in a cross-origin redirect, the browser must discard any earlier 103 hints for security reasons.
