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The 101 Switching Protocols Status Code: A Deep Dive into HTTP Status Code 101

Anchal Rastogi
~ 6 min read | Published on Mar 28, 2024


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What is a 101 Status Code?

In the vast universe of HTTP status codes, the 101 status code, also known as "Switching Protocols," is a gem that often flies under the radar. This status code indicates that the server is switching protocols as requested by the client, typically in response to an Upgrade request header. It signifies a successful handshake between the client and the server, paving the way for a transition to a different protocol.

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What Are the Possible Use Cases for 101 Status Code?

WebSocket Upgrade:

One of the primary applications of the 101 status code is in upgrading an HTTP connection to a WebSocket connection. This upgrade is crucial for real-time communication between the client and server, facilitating tasks such as live chat, gaming, or collaborative editing.

Protocol Switching:

The 101 status code can also be employed when a client wishes to switch to a different communication protocol with the server. For instance, upgrading from HTTP to a custom or more efficient protocol for specific operations.

How to Implement 101 Status Code in JavaScript

Implementing the 101 status code in JavaScript involves responding to a client's Upgrade request appropriately. Here's a simplified example using Node.js and the Express framework:

const express = require('express');
const app = express();

app.get('/upgrade', (req, res) => {
  // Check for Upgrade header in the request
  if (req.headers.upgrade && req.headers.upgrade.toLowerCase() === 'websocket') {
    // Respond with 101 status code and appropriate headers
    res.writeHead(101, {
      'Connection': 'Upgrade',
      'Upgrade': 'websocket'
  } else {
    // Handle other cases
    res.status(400).send('Bad Request');

app.listen(3000, () => {
  console.log('Server listening on port 3000');

Best Practices for Using 101 Status Code

Ensure Compatibility:

Before implementing the 101 status code, ensure that both the client and server support the protocol switching or WebSocket upgrade.

Proper Handshake:

Follow the protocol specifications diligently to ensure a successful handshake between the client and server. Any deviation may lead to errors or connection failures.

How to Test 101 Status Code on Postman

Testing the 101 status code on Postman is straightforward. Simply send a request with the appropriate Upgrade header to trigger the protocol switch or WebSocket upgrade. Postman will display the response with the 101 status code if the server handles the request correctly.

How to Test 101 Status Code in DevTools Browser in Chrome

To test the 101 status code in Chrome DevTools:

  1. Open Chrome DevTools by pressing F12 or right-clicking on the page and selecting "Inspect."
  2. Navigate to the "Network" tab.
  3. Send a request that triggers the 101 status code.
  4. Check the response headers in the Network tab. The response with the 101 status code should be visible.

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Frequently Asked Questions

Q: Can I use the 101 status code for HTTP/2 upgrade?

A: No, the 101 status code is not intended for HTTP/2 upgrade. Instead, HTTP/2 upgrade is handled through other mechanisms specified in the HTTP/2 protocol.

Q: What happens if a client doesn't support the protocol switch?

A: If a client doesn't support the protocol switch indicated by the 101 status code, it may either ignore the response or handle it as a connection error.

Q: Is it mandatory to include the Upgrade header in the client request?

A: Yes, the Upgrade header is essential for initiating the protocol switch or WebSocket upgrade. Without it, the server won't recognize the client's intention to switch protocols.

Q: Can servers downgrade protocols using the 101 status code?

A: No, the 101 status code is specifically for upgrading protocols. Downgrading protocols would require a different approach or status code.

Q: Are there security considerations when using the 101 status code?

A: Yes, security considerations arise when switching protocols, especially if sensitive information is transmitted. Implementing secure protocols and validating client requests are crucial for maintaining security.


In the realm of HTTP status codes, the 101 status code, often overlooked, plays a vital role in facilitating protocol switching and WebSocket upgrades. Understanding its nuances and implementation best practices can enhance communication efficiency between clients and servers. For seamless error monitoring and handling, consider leveraging Zipy's tool, which offers session replay capabilities. Explore more at Zipy for efficient error management.

Read more resources on 1xx status codes

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