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Decoding the 401 Unauthorized Status Code - HTTP Error Code 401

Karthik MSN
~ 7 min read | Published on Mar 28, 2024


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In the realm of web development, encountering HTTP status codes is inevitable. Among these, the 401 Unauthorized status code is one that frequently pops up, often leaving developers puzzled. In this comprehensive guide, we'll delve into what the 401 error signifies, explore its possible causes, discuss handling strategies in JavaScript, outline best practices, and offer practical methods for testing the code. Let's unravel the mysteries behind the 401 error together.

What is a 401 error?

The 401 Unauthorized status code indicates that the request lacks valid authentication credentials. In simpler terms, the server understands the client's request but refuses to fulfill it because the user making the request has not been authenticated or lacks proper authorization credentials. It's essentially the server's way of saying, "You're not allowed to access this resource."

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What are the possible causes for 401 error?

Several factors could trigger a 401 error:

  1. Missing or Incorrect Credentials: If the user fails to provide the necessary credentials or provides invalid ones, the server responds with a 401 error.
  2. Expired Session: Sometimes, the user's session might expire between requests, leading to a 401 response when attempting to access protected resources.
  3. Insufficient Permissions: The user might lack the necessary permissions to access the requested resource, resulting in a 401 error.
  4. Authentication Token Issues: If there's an issue with the authentication token, such as it being revoked or improperly generated, the server may return a 401 status.

How to handle 401 in JavaScript

Handling 401 errors in JavaScript involves implementing appropriate logic to deal with authentication failures gracefully. Here's a basic example using Axios:

  .then(response => {
    // Handle successful response
  .catch(error => {
    if (error.response.status === 401) {
      // Redirect to login page or prompt user to authenticate
    } else {
      // Handle other errors

In this snippet, we intercept the error response and check if the status is 401. If so, we can redirect the user to the login page or prompt them to authenticate.

Best Practices for using 401 status code

When working with the 401 status code, consider the following best practices:

  1. Provide Clear Error Messages: Inform users why their authentication failed and guide them on how to rectify the issue.
  2. Use HTTPS: Ensure that authentication credentials are transmitted securely over HTTPS to prevent interception by malicious parties.
  3. Implement Token Expiry: Employ token expiration mechanisms to mitigate the risk of unauthorized access due to prolonged session validity.
  4. Utilize Refresh Tokens: Implement refresh tokens to obtain new authentication tokens without requiring the user to re-enter their credentials.

How to test 401 status code on Postman

Testing the 401 status code in Postman is straightforward:

  1. Open Postman and create a new request for the endpoint you want to test.
  2. Go to the "Authorization" tab and choose the type of authentication (e.g., Basic, Bearer Token).
  3. Enter invalid credentials or omit them altogether.
  4. Send the request and observe the response. A 401 Unauthorized status indicates a successful test.

How to test 401 status code in DevTools browser in Chrome

Testing the 401 status code using Chrome DevTools is also simple:

  1. Open Chrome and navigate to the page you want to test.
  2. Open DevTools by pressing F12 or right-clicking on the page and selecting "Inspect."
  3. Go to the "Network" tab.
  4. Perform the action that triggers the authentication request.
  5. Look for the request in the network activity list.
  6. Check the response status. A 401 status indicates the test was successful.

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Frequently Asked Questions

Q: What should I do if I encounter a 401 error?

A: First, double-check your authentication credentials to ensure they are correct and up-to-date. If the issue persists, contact the system administrator or refer to the documentation for troubleshooting steps.

Q: Can a 401 error occur even if I'm logged in?

A: Yes, a 401 error can occur if your session has expired, your credentials are invalid, or you lack the necessary permissions to access the resource.

Q: How can I prevent 401 errors in my application?

A: To prevent 401 errors, ensure that users are properly authenticated and authorized before accessing protected resources. Implementing robust authentication mechanisms and handling expired sessions effectively can help mitigate these errors.

Q: What's the difference between 401 and 403 errors?

A: While both indicate access denial, a 401 error means the request lacks valid authentication credentials, whereas a 403 error means the server understood the request but refuses to authorize it, even with valid credentials.

Q: Is it safe to include sensitive information in a 401 error response?

A: No, it's not recommended to include sensitive information in a 401 error response, as it could potentially leak sensitive data to unauthorized users. Keep error responses concise and avoid disclosing unnecessary details.


Navigating the complexities of the 401 Unauthorized status code is crucial for web developers and IT professionals alike. By understanding its nuances, possible causes, and best practices for handling and testing, you can ensure a smoother authentication experience for your users. For a comprehensive tool that aids in monitoring and handling errors, including 401 responses, consider leveraging Zipy's session replay capabilities. Learn more about Zipy here.

Read more resources on 4xx error status codes

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