Getting Ahead of the Curve: Testing Your Site for HTTP/3 Readiness

Hey there! If you‘re a technical leader or developer responsible for a website, you‘ve likely heard about HTTP/3 by now. This latest revision of the HTTP protocol promises faster page loads, reduced latency, and improved security. With Chrome, Firefox and Cloudflare already onboard, HTTP/3 capable clients are coming sooner than you think.

So how can you test if your site is ready? This comprehensive guide has you covered with several easy methods. I‘ll also share performance gains you can expect, when to implement HTTP/3, and even downsides to be aware of.

Let‘s start with a quick primer so you know exactly why HTTP/3 matters:

Why HTTP/3 Matters

HTTP powers communication between browsers and websites. When you enter a URL, an HTTP request is made to the server to load the page and assets.

HTTP/3 specifically introduces two major improvements:

  1. It‘s based on the new QUIC transport protocol instead of TCP. QUIC offers:

    • Dramatically reduced connection establishment latency. Pages start loading almost instantly.
    • Multiplexing of different types of data over a single connection.
    • Mandatory encryption for enhanced security.
  2. It uses the latest TLS 1.3 encryption by default for secure 0-RTT handshakes.

As a result, HTTP/3 delivers up to 60% faster page load speeds compared to HTTP/2:

Protocol Page Load Time
HTTP/1.1 5.9s
HTTP/2 3.6s
HTTP/3 2.9s

(Synthetic brower benchmark by Cloudflare)

Additionally, moving to HTTP/3 may improve your search engine rankings as Google has signaled prioritizing pages served over modern protocols.

Now that you know the benefits, let‘s explore popular techniques to validate whether your website already supports HTTP/3 or not.

Browser-based Testing

Enabling a few hidden settings in Firefox Nightly or Chrome Canary allows early testing of HTTP/3 functionality…

// Instructions for Firefox, Chrome Canary etc

I‘d suggest verifying in both browsers for consistency across early QUIC implementations.

To confirm HTTP/3 support, you need to see h3-?? or HTTP/3 in the protocol version – not just QUIC. Here are examples of positive test results:

Firefox showing HTTP/3 enabled

Figure 1. Firefox Nightly confirming HTTP/3 support

Chrome Canary showing protocol version with QUIC+HTTP3

Figure 2. Chrome Canary output for a compatible site

If you only see QUIC mentioned, that indicates Google‘s Original QUIC – not the IETF HTTP/3 standard. While this features some benefits like encryption, you won‘t get the full speed gains of HTTP/3 without an upgrade.

Web-based Testing Tools

If dealing with browser testing seems complicated, free online tools offer simpler HTTP/3 checking:

Domsignal uses cURL to validate HTTP/3 capability, providing clear results:

Domsignal validation output

Figure 3. Domsignal validator showing HTTP/3 is enabled

Similarly, validates HTTPS/QUIC support:

http3check reporting positive result

Figure 4. HTTPS3Check verification output

These online checkers offer an effortless way to confirm if your site can serve HTTP/3 requests.

Terminal Testing Methods

If you prefer command line tools, there are a couple options:

Latest cURL

Recent versions of cURL include native HTTP/3 support using the --http3 flag:

curl --http3 -I

Geekflare API

Geekflare offers an HTTP Protocol API to programmatically check site compatibility.

After signing up for a free tier API key, you can test like so:

curl \ 
  -H "Authorization: Bearer API_KEY"


  "ip": "",
  "http_1_1": true,
  "http_2": true,
  "http_3": true   // HTTP/3 enabled!

The free plan allows ~3,000 checks/month – handy for large-scale site reporting.

Implementation Guidelines

Once you‘ve confirmed HTTP/3 readiness, what‘s next?

Here are tips for rolling out support safely:

  • Update your front-end servers/reverse proxies first, then test rigorously before full production rollout.
  • Analyze real-world performance impacts with web vitals and Lighthouse audits.
  • Temporarily A/B test enabling HTTP/3 for a percentage of traffic to compare metrics.
  • If implementing on a CDN, use dynamic steering to gracefully fall back to HTTP/2 if needed.

Based on results, incrementally ramp up the proportion of requests served over HTTP/3.

Take the rollout slow – benefits like 60%+ faster page loads speak for themselves once tuned properly.

Current Adoption Status

HTTP/3 is just emerging as a draft spec, but rapidly gaining support:

Software HTTP/3 Status
Chrome Enabled in Canary & Beta trials
Firefox Included in Nightly versions
cURL Added in v7.75
OpenSSL QUIC & 0-RTT support
Cloudflare HTTP/3 released to all users
Fastly Limited availability
Akamai In client testing

(As of March 2023)

Cloudflare saw ~150% higher revisitation for HTTP/3 sites indicating strong user retention – that‘s a massive growth opportunity!

Given rapid browser adoption, I‘d recommend evaluating HTTP/3 in test environments now to ensure a smooth user transition.

Limitations and Downsides

Being an emerging spec, HTTP/3 deployment isn‘t without some headaches. Limitations to note:

  • Operating system kernel updates required for some servers to enable QUIC
  • Most traditional web frameworks don‘t support HTTP/3 yet
  • Potentially limited firewall/proxy support depending on hardware
  • Extra debugging and instrumentation needed for metrics
  • Additional server load to run TLS 1.3 encryption

For these reasons you may prefer to stage a gradual rollout on less critical properties, rather than hastily upgrading your entire estate.

Monitor for production issues, gather performance data, and expand support once stable. With extra diligence upfront, you‘ll ensure a seamless experience for visitors as HTTP/3 becomes widespread.

Key Takeaways and Next Steps

We‘ve covered a lot of ground explaining the importance of testing your website for HTTP/3 compatibility.

Here are the key takeaways:

✅ HTTP/3 offers very meaningful speed and user experience improvements including 60%+ faster page loads driven by the new QUIC protocol.

✅ To validate if your site supports HTTP/3, use browser debugging, online tools like Domsignal and or terminal methods.

✅ For safe implementation, take an incremental rollout approach while monitoring for production issues.

✅ As browser support rapidly emerges in 2023, websites will need to enable HTTP/3 to stay competitive performance-wise.

Hopefully this guide gives you confidence in upgrading wisely. Reach out via the comments if you have any other questions!

I‘m aiming to evolve this resource into a comprehensive reference on all things HTTP/3, so please share any feedback to improve coverage.

Let‘s work together to build the next generation of faster, safer websites.