When we talk about HTTP response status codes, most people think of common ones like 404 or 200. But there’s a lesser-known category that’s just as important in certain contexts: the 1xx response code class.
In this article, we’ll break down what a 1xx status code is, how it works, and why understanding 1xx HTTP status codes matters—especially for developers and performance testers.
What Is a 1xx Status Code?
A 1xx status code is part of the informational responses in the HTTP response status codes spectrum. These codes indicate that the initial part of a request has been received and the server is still processing it.
Think of a 1xx response code as the server saying, “Hang on, I got your request-processing now.”
These codes aren’t usually visible to users but play an important role in how browsers, proxies, and servers communicate behind the scenes.
When Are 1xx HTTP Status Codes Used?
The 1xx HTTP status code class is used early in the request lifecycle. They’re useful when large or complex requests are being made—especially when protocols like HTTP/1.1 or HTTP/2 are involved.
They’re also important for tools like load testers and performance monitoring platforms that need to interpret every stage of a request.
In most standard web interactions, you won’t see a 1xx status code in action. But in edge cases or during debugging, these codes can give developers useful signals.
Types of 1xx Response Codes
Here are the most common 1xx response codes you might come across:
100 Continue
This is the most frequently seen 1xx HTTP status code. It means the server has received the request headers and is waiting for the body. It’s a green light to continue sending data.
Use case: Large POST or PUT requests. The client checks with the server before sending the full payload.
101 Switching Protocols
This tells the client that the server is switching to a different protocol, such as WebSockets or HTTP/2, based on the request.
Use case: Real-time communication apps or performance-optimized protocols.
102 Processing (WebDAV)
This code is used to indicate that the server has received and is processing the request, but there is no response yet.
Use case: Long-running operations in distributed systems.
103 Early Hints
This newer 1xx status code allows the server to send preliminary headers before the full response is ready. It’s mainly used to help browsers begin loading assets sooner.
Use case: Performance optimization for page speed and SEO.
Why 1xx Response Codes Matter
Even though these 1xx HTTP status codes are rarely seen by end users, they serve several purposes:
- Performance Tuning: 100 and 103 codes help optimize data transfers and improve load times.
- Protocol Negotiation: 101 enables smoother transitions between HTTP and WebSocket or HTTP/2.
- Transparency in Processing: 102 shows that the server is working, which helps in long-running tasks.
Ignoring these signals can cause misunderstandings between client and server, potentially slowing things down or leading to misfires.
How to Monitor and Test 1xx Status Codes
Most basic browser tools won’t show 1xx response codes by default. But here’s how you can track them:
- Browser Dev Tools (Network tab): Some browsers show 1xx status codes if you expand full request/response headers.
- Curl: Use the -i flag to see informational responses in terminal-based HTTP requests.
- Testing Tools: Platforms like Frugal Testing specialize in load testing and often surface these early response codes during analysis.
Should You Worry About 1xx Codes?
For everyday site maintenance? No.
For developers, DevOps engineers, and testers? Absolutely.
Understanding 1xx response codes can:
- Help debug connection delays.
- Improve time-to-first-byte (TTFB) scores.
- Optimize server-client communication, especially under load.
Final Thoughts
1xx status codes might be the quiet operators of the HTTP response status codes family, but they’re far from irrelevant. They provide critical handshake signals between client and server that ensure smoother communication and better performance—especially when milliseconds count.
If you’re diving deep into server logs, building real-time apps, or performance tuning under heavy load, don’t ignore the 1xx HTTP status code family.
Need help understanding how your server handles response codes or optimizing request cycles? Reach out through our performance tuning services or browse our blog for more deep dives.
