Key Ideas:
- Avoid code bloat by testing strategically, not constantly, and use tools like RUMvision and Datadog to monitor performance in real time.
- Leverage Google’s CrUX and Lighthouse for SEO insights while using RUM data to ensure your users are getting the best real-time experience.
- Apply Specific, Measurable, Achievable, Relevant, and Time-bound (SMART) goals to CRO testing for structured, meaningful results.
When improving website performance, many marketers rely on tools like A/B testing, heatmaps, and consent management platforms (CMPs). These tools can provide valuable insights, but they often come with a hidden cost: a direct impact on your website’s speed and performance. Marketers understandably don’t want to hear that the tools they rely on for growth might contribute to sluggish load times and lower Core Web Vitals scores.
But ignoring the problem will not make it go away. Here’s how to approach it with balance: Leverage the data-driven insights you need while keeping your site fast and user-friendly.
The Performance Impact of A/B Testing, Heatmaps, and CMPs
From First Contentful Paint (FCP) to Largest Contentful Paint (LCP), performance bottlenecks often stem from third-party scripts. A/B testing, heatmap tools, and cookie consent banners are among the biggest offenders. And while these tools provide crucial data, it’s important to understand their impact on web performance.
A/B testing tools, for instance, can delay the rendering of critical content. Heatmaps, which track user interactions, are notorious for hogging resources. Cookie consent banners also interfere with user experience metrics like Interaction with Next Paint and LCP.
Monitoring Core Web Vitals in Real Time with Real User Monitoring
This is where real-time performance monitoring tools like RUMvision and Datadog come in. Real User Monitoring (RUM) allows you to see the true impact of these third-party tools on your site’s performance. Rather than guessing whether a script is slowing down your site, RUM lets you monitor actual user experiences and track how performance changes over time.
These services’ ability to benchmark helps you make informed decisions. It’s not about removing the tools you need but about managing and optimizing them. If an A/B testing tool is dragging down your performance, maybe it’s time to try alternatives or place tighter limits on testing times.
My Experience with Datadog: How I Monitored Performance In-House
While working in-house, I relied on Datadog to help monitor performance over time, especially during developer and product rollouts. Tracking Core Web Vitals and page speed elements over time, alongside product changes, was invaluable.
Datadog provided visibility into how updates—whether from the development team or external scripts—affected user experience. It also allowed us to react quickly if new deployments led to performance issues, ensuring that performance monitoring wasn’t just a one-time check but an ongoing part of our optimization strategy.
Smart Testing Over Constant Testing
The issue with “Always Be Testing” (ABT) is that it can often lead to code bloat, performance degradation, and user frustration. To avoid these pitfalls, testing smartly rather than constantly is essential. This means focusing on a more strategic approach:
- Understanding the independent variables you’re testing, such as elements you control like design changes.
- Recognizing the dependent variables, which are outcomes like conversion rates that change based on your tests.
- Consider categorical variables, such as user segments, device types, and, yes, even seasonality, which can impact the results in nuanced ways.
Rather than running tests endlessly and piling on unnecessary code, the goal should be to test strategically. Once you find a winning variation, implement it, and measure the prolonged impact on performance before jumping into the next test. RUM tools are essential in helping you monitor performance over time, ensuring you’re making sustainable improvements that benefit your site’s performance.
Applying SMART Goals to CRO
SMART goals are a well-known framework in Human Resources Management, designed to ensure that goals are Specific, Measurable, Achievable, Relevant, and Time-bound. Applying these principles to Conversion Rate Optimization (CRO) testing helps structure your experiments and avoids the “Always Be Testing” trap:
- Specific: Each test should focus on one clear hypothesis or question. For example, rather than simply testing “button color,” your goal might be, “Does changing the CTA button to green improve conversion rates by 10% on the pricing page?”
- Measurable: Define how you’ll measure success upfront. For CRO, this typically involves metrics like conversion, click-through, or bounce rates. Using RUM tools helps ensure you can track these metrics alongside performance indicators like page speed.
- Achievable: Don’t set yourself up for failure by aiming for unrealistic gains. A goal of “increasing conversions by 5% within the next month” is more achievable than “doubling conversions overnight.” Ensure your team has the resources to conduct the test and analyze its impact.
- Relevant: Make sure your tests align with business goals. Testing for the sake of testing creates unnecessary complexity. If the goal is to drive more sign-ups, focus on optimizing the sign-up flow, not on minor aesthetic tweaks that don’t impact the more extensive user journey.
- Time-bound: Set clear time frames for your tests and measure performance over these periods. For example, run your test for two weeks, then analyze the results and implement changes if successful. Once a winning variation is rolled out, continue to monitor its rolled-out performance over time before launching a new test.
By applying SMART goals to your CRO efforts, you avoid the pitfalls of endless testing and code bloat. This structured approach ensures you’re making meaningful, measurable improvements, rather than simply adding more complexity to your site.
Use Data to Improve, Not Overload
Ultimately, the goal is to strike a balance. Your analytics, CRO tools, and consent management platforms are vital for improving conversions, but they should not burden your site’s performance. Test smartly, use real-time monitoring tools like RUMvision and Datadog, and roll out changes that truly benefit both your users and your bottom line.
Your site’s speed and usability matter just as much as the insights you gain—don’t sacrifice one for the other.
What About CrUX and Lighthouse Data?
“OK, Scott. But what about CrUX data from the Chrome User Experience Report and Lighthouse? That’s what Google uses!” And yes, you’re absolutely right. These tools—particularly Lighthouse—are foundational to understanding how Google views your site’s performance. But there’s an important distinction to make here.
CrUX and Lighthouse provide valuable insights, specifically on how users experience your site in terms of Core Web Vitals, as measured by Google. These metrics are crucial for SEO and aligning with Google’s expectations for site speed, stability, and interactivity. However, tools like RUMvision and Datadog serve a different purpose. They give you real-time, user-specific data based on how people interact with your site, which is invaluable for understanding what’s happening in the moment—not just what a Google-driven dataset tells you.
Why You Need Both CrUX and RUM Data
It’s important to note that committing to using RUM tools means accepting that you will be looking at numbers that Google isn’t looking at. RUM tools give you granular insights on your audience’s actual experience, whereas CrUX and Lighthouse provide benchmarks based on a broader view of performance across all Chrome users.
Both datasets are important, but for different reasons:
- CrUX and Lighthouse: These provide insights on how Google sees your site’s performance. They’re important for SEO and ensuring that your Core Web Vitals meet Google’s thresholds. They’re also helpful for broad benchmarks against your competition.
- RUM tools: These give you real-time performance insights for your actual users, based on their unique experiences. You can track how product rollouts, new tests, and third-party scripts affect your specific audience’s interaction with your site.
Don’t Sacrifice Performance for SEO Alone
It’s tempting to focus solely on Google’s view of your site and try to “fix” everything according to those scores. But unless more than 51% of your users are coming directly from Google, don’t fall into the trap of over-optimizing just for SEO.
Your website should serve your users first—not just Google’s algorithms. RUM data helps you keep that balance, ensuring you’re not sacrificing your users’ actual experience in pursuit of perfect CrUX scores.
Use both datasets for their specific purposes: CrUX and Lighthouse to keep your SEO performance in check, and RUM tools to ensure your users are getting the best experience in real time. By treating each dataset as a piece of the puzzle, you can create a site that performs well both for search engines and the people who matter most—your users.