1xx Informational HTTP Codes
The 1xx (Informational) class of HTTP status codes indicates a provisional response consisting only of the status line and optional headers, terminated by an empty line. These codes inform the client that the initial request was received and that the server is continuing the operation or negotiating protocol upgrades.
Continue
The server has received the request headers and the client should proceed to send the request body.
Switching Protocols
The requester has asked the server to switch protocols and the server has agreed to do so.
Processing
A WebDAV request may contain many sub-requests involving file operations, requiring a long time to complete.
Early Hints
Used to return some response headers before final HTTP message.
💡Understanding 1xx Informational Codes
Why These Status Codes Matter
While rarely visible in standard browser navigation, 1xx status codes are essential for high-performance protocols—enabling large file uploads without wasted bandwidth (100 Continue), real-time bidirectional WebSockets (101 Switching Protocols), and early resource preloading (103 Early Hints).
Diagnostic & Troubleshooting Strategy
Check your HTTP protocol version (HTTP/1.1 vs HTTP/2), verify reverse proxy upgrade headers (like Nginx proxy_set_header Upgrade), and inspect raw network headers in Wireshark or browser DevTools.
Frequently Asked Questions About 1xx Codes
What does a 1xx status code mean?
A 1xx status code is an informational response indicating that the server has received the request headers and the client should continue sending the request body or proceed with protocol negotiation.
Do browsers display 1xx status codes to users?
No, browsers handle 1xx codes internally in the networking layer. You can observe them in browser DevTools (Network tab) or server diagnostic logs.
Why is 103 Early Hints important for SEO?
103 Early Hints allows web servers to inform browsers about critical CSS, fonts, and scripts to preload while the server is still rendering HTML, significantly improving Largest Contentful Paint (LCP) and Core Web Vitals.