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What Is a http error 406 Status code?

http error 406

In the vast and intricate world of web development, HTTP status codes play a crucial role in communication between clients and servers. These three-digit codes convey information about a client’s request’s success, failure, or redirection. 

Among these status codes, the 406 status code stands out as a specific indicator that carries valuable insights about the interaction between the client and server.

In this blog post, we will delve into the depths of the 406 status code, exploring its meaning, significance, and the scenarios it encounters.

What is the http error 406 Status Code?

HTTP status codes are standardized responses that servers use to communicate with clients. The 406 status code, also known as “Not Acceptable,” is one such response that the server sends to the client when the requested resource cannot be served in a format that complies with the client’s specific preferences, as indicated in the request’s ‘Accept’ header.

What Causes HTTP error 406 Status Code?

Incompatible Content Types

One common reason for encountering a 406 error is when the server cannot generate content in a format acceptable to the client. It can happen if the client specifies certain content types and the server cannot meet those criteria.

Lack of Content Negotiation Support

The 406 Not Acceptable status code often arises when the server doesn’t support content negotiation. Content negotiation is the process through which the server selects the appropriate resource representation based on the client’s preferences expressed in the request’s headers.

Misconfigured Server

Misconfigurations on the server side can also generate http error 406 status code. It might include incorrect configurations related to supported content types or problems with content negotiation settings.

Understanding the Request-Response Cycle:

To fully comprehend the 406 status code, let’s first examine the basic structure of the request-response cycle in the HTTP protocol.

Client Sends a Request:

When a user interacts with a web application, the client (usually a browser) sends a request to the server for a particular resource.

Server Processes the Request:

The server receives the request and processes it to determine the appropriate response.

Server Sends a Response:

Based on the server’s processing, it sends back an HTTP response to the client. This response includes an HTTP status code and additional information as necessary.

The Role of the ‘Accept’ Header

The ‘Accept’ header is a crucial component of an HTTP request that plays a pivotal role in content negotiation between the client and server. It informs the server about the media types, such as text, image, or application, that the client can understand. 

This header is particularly relevant when clients prefer a specific resource representation, like JSON or XML.

Interpreting the 406 Status Code

When a client receives a 406 status code in response to its request, it implies that the server acknowledges the request but cannot fulfill it per the client’s expectations.

The client is, therefore, informed that the resource’s representation it seeks is not available or not acceptable in the specified format.

Common Scenarios Leading to HTTP error 406 Status Code

A 406 Not Acceptable status code could be due to any one or more of the following reasons:

  • Requested Resource Not Available in Requested Format: The client may have failed to request a resource (like files or web pages) that isn’t currently supported on their server.
  • Unsupported Accept header: When making requests from clients, their recommendations may include an Accept header to specify how the server should respond based on what type of response format was requested by their requestors. If the server cannot provide that format, a 406 status code will be returned instead.
  • Unsupported Character Encodings: If the client request contains a Content-Type header that specifies an unsupported character encoding for which no server support exists, a 406 error may result.
  • Mismatched Request and Response Content Types: In some instances, servers cannot deliver responses to the client’s requests due to a content type mismatch between the client’s request and the server’s response.

Error 406 usually indicates that the server could not fulfill a client’s request because of issues related to its requested resource, request headers, or server settings.

Handling the 406 Status Code

An HTTP Error 406 not Acceptable status code indicates that a server could not deliver an acceptable response, as shown in the Accept header of your request.

Below are several potential solutions to solve such an error:

  • Update the Accept header: If the client provides an Accept header in their request, but the server doesn’t support its format, try switching up or even eliminating this Accept header altogether and see if that resolves the problem.
  • Check Server Configuration: Sometimes, your server may lack all the components or configuration to deliver what’s requested in an acceptable format. Check its logs and configuration files to ensure it can produce what’s desired.
  • Add Additional Parameters: Depending on the nature of the use case, requests can often be modified by including additional parameters that enable servers to respond to the desired form precisely. Some APIs permit clients to specify these other parameters via URL parameters for greater flexibility when specifying response formats.
  • Contact the Server Administrator: If the error persists despite taking all these steps, then changes need to be made to either server configuration or API documentation to support desired response formats. Contacting either the administrator or provider could provide further assistance.

Also Read: The importance of page speed in SEO

406 Status Code Impact On Search Engine Optimization

A 406 status code can have severe SEO implications if it prevents search engines from properly indexing or accessing affected resources.

Search engines’ inability to index a resource due to an Error 406 could negatively affect its visibility in SERPs (search engine results pages), reducing traffic and visibility for that page or site. It may ultimately result in decreased visitors to that website.

Users experiencing 406 errors when trying to access specific resources on a site could become dissatisfied and may subsequently recommend other websites, leading to indirect effects on overall SEO.

Real-World Example:

Let’s consider a practical example to illustrate the occurrence of a 406 status code. 

Suppose a client sends the following request header:

GET /api/data HTTP/1.1

Host: example.com

Accept: application/xml

In this case, the client explicitly indicates that it can only accept XML as the response format. 


In the communication between clients and servers on the web, HTTP status codes serve as critical signals. The 406 status code, or “Not Acceptable,” deals explicitly with content negotiation and informs the client that the server cannot provide the requested resource in a format acceptable to the client’s preferences. 

By understanding the essential aspects of the 406 status code, web developers can enhance the quality of their applications, ensuring smoother interactions and improved user experiences. As the digital landscape evolves, a deep understanding of HTTP status codes remains essential to building robust, user-friendly web applications.

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