Implementing Signed Exchanges (SXG) for Speed

In the fast-paced digital world, speed is not just a luxury—it’s a necessity. Websites that load quickly deliver better user experiences, increase engagement, and often improve search engine rankings. As such, developers and businesses are constantly searching for new ways to optimize performance. One of these cutting-edge techniques is the implementation of Signed Exchanges (SXGs). But what exactly are SXGs, and how can they make your site faster? Let’s dive deep into this powerful technology.

What are Signed Exchanges?

Signed Exchanges (SXGs) are a part of the Web Packaging initiative, which allows content to be delivered through third parties—like a search engine cache or content delivery network (CDN)—while preserving the authenticity and privacy of the original publisher.

Normally, when a user clicks on a link in a search engine results page or any third-party source, the content is fetched directly from that origin. Depending on the location of the server and current traffic, this can introduce delays. SXGs allow third parties, such as Google Search, to prefetch and cache your content. This content is then presented instantly to users without compromising security or trust, thanks to the embedded digital signature.

Why Use Signed Exchanges?

Implementing SXGs on your site can provide tremendous benefits:

• Instant Loading: With the ability to prefetch content, pages open almost instantaneously from sources like Google Search.
• SEO Advantage: Fast-loading content can improve your page’s signals related to Core Web Vitals, which are key for search ranking.
• Authenticity: The cryptographic signature ensures that even if the content is served from a third party, it’s been verified as authentic and untampered.
• Improved Privacy: SXGs remove the need for the referrer to know the user who requested the content, enhancing user privacy.

How Signed Exchanges Work

SXGs fundamentally change how web content is retrieved and displayed. Here’s a simplified breakdown of the exchange:

1. A user initiates a query—say, from Google Search.
2. Google search fetches your site’s SXG package and caches it in its own CDN.
3. When a user clicks your page URL, Google serves the preloaded, signed page instantly.
4. The user’s browser verifies the digital signature to ensure authenticity.
5. The browser displays your URL in the address bar—not Google’s—preserving ownership and branding.

This mechanism provides both speed and trust, ensuring users get a seamless experience without having to navigate to your origin server repeatedly.

Requirements for Implementing SXGs

Before diving into implementation, it’s crucial to understand the prerequisites. Setting up SXGs involves several components:

• AMP or Valid HTML: While SXGs originally worked with AMP pages, they now support any valid HTML that complies with prefetch requirements.
• CERT for CanSignHttpExchanges: You’ll need a certificate that supports the CanSignHttpExchanges extension. These are typically issued by services like Let’s Encrypt and DigiCert.
• Private Key Infrastructure: Secure management of private keys is essential to generate valid signatures.
• Packaging Tool: You can use tools like go/sxg or integrations within your CDN environment (e.g., Fastly, Cloudflare) to generate and serve SXGs.

Finally, you’ll need to configure your HTTP headers properly to announce and deliver signed content packages, including headers like Content-Encoding: sxg and Content-Type: application/signed-exchange;v=b3.

Steps to Implement Signed Exchanges

Below is an overview of the steps required to add SXG support to your web application:

1. Acquire an SXG-Capable Certificate: Request a certificate with the CanSignHttpExchanges extension from a trusted Certificate Authority.
2. Prepare Your Web Pages: Ensure your HTML pages are crawlable and suitable for prefetching. Avoid personalization or dynamic content that could yield incorrect or stale results when prefetched.
3. Set Up the SXG Packaging Tool: Install and configure the official Go SXG tool or use a CDN integration that supports SXG packaging.
4. Generate Signed Exchanges: Create signed versions of your HTML pages containing the HTTP response, signature, and validity information.
5. Serve and Declare Support: Implement an alternate version of the page under a well-known path or via HTTP content negotiation. Googlebot must be able to discover and crawl it.

Using a CDN to Simplify SXG Implementation

If this all sounds complicated—fear not. Many modern CDNs such as Cloudflare or Fastly now offer SXG-as-a-Service. These platforms handle the certificate management, content packaging, and delivery. Here’s why this option is appealing:

• Less Infrastructure Overhead: No need to build and manage SXG packaging yourself.
• Automatic Management: CDNs automatically handle key rotation, hashing, and signature expirations.
• Seamless Integration: Just enable the appropriate features and let your CDN manage the complexities in the background.

Common Pitfalls and Best Practices

Implementing SXGs requires attention to detail. Avoid the following pitfalls to ensure your implementation is successful:

• Content Freshness: Ensure your SXG packages are updated frequently to avoid serving stale or incorrect content.
• Security Management: Since SXGs rely on cryptographic signatures, a compromised private key can pose a major security risk. Use HSMs or secured vaults to store these credentials.
• Testing and Validation: Use tools like Google’s SXG Testing Tool to validate that everything is working as expected. Regularly monitor logs and performance metrics.

Additionally, you should communicate in your HTTP headers or robots.txt file that your content supports SXGs, and explicitly allow prefetching and caching by third parties like Googlebot.

Real-World Use Cases

Major companies that have embraced Signed Exchanges have seen measurable performance improvements. For example:

• eBay: Reports faster time-to-interactive (TTI) for product pages appearing in search results.
• The Guardian: Achieved lower bounce rates and higher engagement on prefetched articles.
• Nikkei: One of the first Japanese publishers to adopt SXGs, noted a 38% increase in page views per session.

These results underscore that SXGs are not just theoretical—they deliver real benefits in terms of speed, engagement, and trust.

The Future of Web Performance

SXGs are indicative of the shift toward a more efficient and decentralized web. By enabling content delivery through third parties without sacrificing authenticity, they offer a compelling alternative to traditional HTTP fetching. The growing support from browsers, CDNs, and search engines is expected to push this technology into the mainstream in the coming years.

For developers and site owners committed to performance and optimization, exploring Signed Exchanges is a step in the right direction.

Final Thoughts

Speed matters. Users expect it, and search engines reward it. Signed Exchanges represent a fascinating evolution in how web content is packaged, delivered, and trusted. With relatively low setup barriers—especially using CDNs—now is a great time to experiment and iterate with SXGs on your own site. The ultimate payoff? Faster experiences, happier users, and possibly better rankings.

As we continue moving toward a web experience built on speed, trust, and privacy, SXGs stand as a forward-thinking solution ready to meet those demands.