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Understanding the 501 Not Implemented Error - HTTP Error Code 501

Vishalini Paliwal
~ 6 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 501 Not Implemented Error stands out as one that developers must understand thoroughly to ensure smooth functioning of their web applications. In this comprehensive guide, we will delve into the nuances of the 501 error, exploring its causes, handling methods, best practices, and testing procedures.

What is a 501 Error?

The 501 Not Implemented Error is an HTTP status code indicating that the server does not recognize the request method or lacks the ability to fulfill the request. It implies that the server does not support the functionality required to fulfill the request, often due to the method not being implemented by the server.

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What are the Possible Causes for 501 Error?

Several factors can lead to the occurrence of a 501 error:

  1. Unsupported HTTP Method: One common cause is when the server receives a request with an HTTP method that it does not support or recognize. For instance, if a client sends a request using a custom or deprecated method, the server may respond with a 501 error.
  2. Misconfigured Server: In some cases, misconfigurations on the server side, such as incomplete or outdated server software, can result in the server being unable to process certain types of requests.
  3. Backend Framework Limitations: The web application's backend framework may lack support for certain HTTP methods, leading to the server being unable to fulfill requests that require those methods.

How to Handle 501 in JavaScript

When encountering a 501 error in JavaScript, developers can handle it gracefully by implementing appropriate error-handling mechanisms. Below is an example of how to handle a 501 error using JavaScript's Fetch API:

fetch('<>', {
  method: 'POST',
  body: JSON.stringify(data),
  headers: {
    'Content-Type': 'application/json'
.then(response => {
  if (!response.ok) {
    if (response.status === 501) {
      throw new Error('501 Not Implemented');
    } else {
      throw new Error('HTTP Error: ' + response.status);
  return response.json();
.catch(error => {
  console.error('Error:', error);

Best Practices for Using 501 Status Code

To ensure proper utilization of the 501 status code, developers should adhere to the following best practices:

  1. Provide Informative Error Messages: When returning a 501 status code, include clear and informative error messages that help users understand why the request could not be fulfilled.
  2. Implement Proper Error Handling: Handle 501 errors gracefully in client-side and server-side code to provide a seamless user experience and facilitate troubleshooting.
  3. Regularly Update Server Software: Keep server software up to date to mitigate potential issues related to unsupported HTTP methods and ensure compatibility with modern web standards.

How to Test 501 Status Code on Postman

Postman provides a convenient way to test HTTP status codes, including 501. Follow these steps to test a 501 status code in Postman:

  1. Open Postman and create a new request.
  2. Enter the request URL and select the desired HTTP method.
  3. Send the request.
  4. Check the response status code in the "Status" section of the response panel. If the server responds with a 501 status code, it indicates that the request method is not implemented.

How to Test 501 Status Code in DevTools Browser in Chrome

Testing a 501 status code in the Chrome DevTools browser is straightforward:

  1. Open Chrome DevTools by pressing Ctrl + Shift + I (Windows/Linux) or Cmd + Option + I (Mac).
  2. Navigate to the "Network" tab.
  3. Perform the desired action that triggers the request.
  4. Inspect the network request in the DevTools panel.
  5. Look for the status column to check if the response includes a 501 status code.

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Frequently Asked Questions

Q: How can I fix a 501 Not Implemented Error?

A: To address a 501 error, review the request method being used and ensure that the server supports it. If necessary, update server configurations or modify the request to use a supported method.

Q: Can a client-side script cause a 501 error?

A: Yes, if the client-side script sends a request using an unsupported HTTP method, it can trigger a 501 error from the server.

Q: Is a 501 error permanent or temporary?

A: A 501 error typically indicates a permanent condition where the server does not support the requested functionality. However, server configurations or updates may resolve the issue in some cases.

Q: Does a 501 error affect SEO?

A: While a single occurrence of a 501 error may not have a significant impact on SEO, frequent occurrences or unresolved server issues can negatively affect website performance and search engine rankings.

Q: Are there specific server configurations that commonly trigger a 501 error?

A: Yes, outdated or misconfigured server software, as well as restrictions imposed by server-side frameworks, are common factors contributing to 501 errors.


In conclusion, understanding the nuances of the 501 Not Implemented Error is crucial for web developers and IT professionals alike. By familiarizing themselves with its causes, handling methods, and best practices, developers can ensure smoother operation of their web applications and enhance the overall user experience. For effective monitoring and handling of errors, including 501 errors, consider leveraging Zipy's comprehensive tool with session replay capabilities. Learn more at Zipy.

Read more resources on 5xx error status codes

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