Robotecture » HTTP » HTTP Headers » Sec-CH-UA-Arch

Sec-CH-UA-Arch Header: Overview

In this post, we’ll dive into the world of Sec-CH-UA-Arch headers, providing you with all the necessary information to understand, implement, and leverage this technology effectively. We’ll begin by exploring the background and context of client hints and User-Agent strings, followed by an in-depth look at the Sec-CH-UA-Arch header itself. Along the way, we’ll share real-world examples, best practices, and potential issues you may encounter.

Background and Context

Client hints are a set of HTTP request headers that provide information about a user’s device and preferences. These hints allow servers to optimize content delivery based on the specific characteristics of each user’s environment, ensuring a tailored and efficient browsing experience.

The User Agent client hints is an HTTP header that provides information about the user’s browser, operating system, and device. This information is used by web servers to tailor content to the user’s environment, enabling compatibility and optimization.

What is Sec-CH-UA-Arch Header?

The Sec-CH-UA-Arch header is an HTTP request header that provides information about the user’s device CPU architecture. It is part of the User-Agent Client Hints (UACH) initiative, which aims to address the limitations of traditional User-Agent strings by offering a more structured and privacy-preserving way to share user information with web servers. The primary purpose of the Sec-CH-UA-Arch header is to allow servers to optimize content delivery based on the user’s specific CPU architecture, potentially leading to improved performance and user experience.


Architecture Token

The Sec-CH-UA-Arch header contains a single token representing the user’s device CPU architecture. This token is a string that succinctly identifies the type of processor in use, allowing servers to make informed decisions about how to deliver content.

Possible Values

Some common values for the Sec-CH-UA-Arch header include:

  1. x86: Represents Intel x86 and compatible processors, commonly found in desktops, laptops, and some server systems.
  2. ARM: Represents ARM processors, typically found in mobile devices, tablets, and some embedded systems.
  3. MIPS: Represents MIPS processors, often used in networking equipment and embedded devices.
  4. PPC: Represents PowerPC processors, used in some embedded systems and historically in Apple computers.

Keep in mind that this list is not exhaustive, and new processor architectures may be added over time.

Use Cases

The Sec-CH-UA-Arch header can be leveraged in various ways, including:

  • Optimizing Web Content Delivery: Web servers can use the Sec-CH-UA-Arch header to deliver optimized content for specific CPU architectures. For example, a server might deliver different JavaScript code or WebAssembly modules based on the user’s processor, ensuring that the code runs efficiently on their device.
  • Enhancing User Experience: By understanding the user’s CPU architecture, web developers can design and deliver content tailored to the user’s device capabilities. This can lead to improved performance and a better overall user experience, as content is specifically optimized for the user’s hardware.
  • Security and Privacy Implications: The introduction of the Sec-CH-UA-Arch header can help reduce reliance on traditional User-Agent strings, which are often verbose and prone to inaccuracies. By providing a more structured and privacy-preserving way to share user information, the Sec-CH-UA-Arch header can contribute to a safer and more private browsing experience. However, it is essential to use this header responsibly and avoid unnecessary data collection to respect users’ privacy.

Setting up Sec-CH-UA-Arch Header

Server-side Configuration

To use the Sec-CH-UA-Arch header in your web application, you first need to configure your server to accept and process the header. This process may vary depending on your server software. Here’s an example for the popular web server, Nginx:

  1. Open your Nginx configuration file (e.g., nginx.conf).
  2. Locate the http or server block and add the following line to enable the Sec-CH-UA-Arch header:
add_header Accept-CH "Sec-CH-UA-Arch";
  1. Save the configuration file and restart the Nginx server.

For other server software, consult their respective documentation for enabling client hints.

Client-side JavaScript

Once your server is configured to accept the Sec-CH-UA-Arch header, you can access the header value in your client-side JavaScript code using the navigator.userAgentData object:

if (navigator.userAgentData) {
    .then(uaData => {
      console.log("CPU Architecture:", uaData.architecture);
    .catch(error => {
      console.error("Error fetching CPU architecture:", error);
} else {
  console.warn("User-Agent Client Hints not supported in this browser.");

This code snippet first checks if the browser supports User-Agent Client Hints. If supported, it retrieves the CPU architecture and logs it to the console.

Best Practices

When working with the Sec-CH-UA-Arch header, consider the following best practices:

Data Minimization

Collect and use only the data you need to optimize your web application. Excessive data collection can raise privacy concerns and may even violate data protection regulations. When using the Sec-CH-UA-Arch header, focus on the specific use cases where understanding the user’s CPU architecture can enhance performance or user experience.

Graceful Degradation

Ensure that your web application continues to function correctly even when the Sec-CH-UA-Arch header is unavailable or unsupported. Implement fallback mechanisms to deliver content that works well on a broad range of devices, without relying solely on the information provided by the header.

Browser Compatibility

Keep in mind that not all browsers support the Sec-CH-UA-Arch header or User-Agent Client Hints in general. Test your web application across various browsers to ensure it works as expected, regardless of support for these features. You can use feature detection, as shown in the client-side JavaScript exam

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