Yes—A/B testing can affect Core Web Vitals, but the impact depends on how visitors are assigned to a variant and what that variant changes. A client-side tool that delays showing a page can hurt Largest Contentful Paint (LCP); content inserted or repositioned without reserving space can contribute to Cumulative Layout Shift (CLS). A/B testing does not automatically worsen every metric, so compare real-user results between experiment groups.
How an A/B test can change Core Web Vitals
Largest Contentful Paint (LCP)
Some client-side testing tools wait to display a page until they identify the visitor’s group and apply the variant. This can delay when the page’s largest visible content appears, worsening LCP. Assigning the variant on the server can avoid that particular client-side delay. Google recommends understanding how a test is applied, limiting it to relevant pages and a subset of users, and removing it when it is no longer needed. Google’s A/B testing guidance and business-impact guidance discuss the performance trade-off.
Cumulative Layout Shift (CLS)
A variant may add, remove, or reposition page elements. If content loads later and pushes existing content aside—or the page does not reserve space for newly inserted content—the change can contribute to CLS. Check the actual variant behavior rather than assuming that the test itself caused a shift. Google’s implementation guidance explains how experiments can affect rendering.
Interaction to Next Paint (INP)
INP measures responsiveness to user interactions, but an A/B test does not necessarily make it worse. To identify an effect, compare real interaction data by variant and inspect whether the variant adds main-thread work or changes the interactions users perform. A page-load lab run alone cannot establish the experience of real interactions. Google’s Web Vitals guidance describes INP and its field-data context.
Free tools Windows power users keep installed
One-click scans. No signup required.
#1 Best Overall
- Read Before You Buy — No Video Output: These adapters support charging and USB 2.0 data transfer, but cannot transmit video signals. Except for standard USB webcams (which use USB data only), they are not compatible with HDMI/DisplayPort cables, video-capable USB-C hubs, or docking stations with video output.
- Convert USB-A Ports to USB-C: Designed to connect USB-C earphones, cables, flash drives, card readers, and other USB-C accessories to standard USB-A ports. Plug-and-play with no drivers or software required.
- Aluminum Alloy Housing: Built with a sturdy aluminum alloy shell that aids in heat dissipation and protects against daily wear and scratches. Designed to maintain a stable and secure connection.
- Compact & Travel-Friendly: The ultra-compact design allows the adapter to stay plugged into your device without blocking adjacent ports or adding bulk, reducing wear and tear on your original USB ports.
- 12-Month Warranty: Backed by a 12-month manufacturer warranty for peace of mind. Designed to meet strict quality control standards for reliable everyday performance.
What counts as a good Core Web Vitals result?
Google’s current Core Web Vitals are LCP, INP, and CLS. A result is considered good when it meets all three thresholds below at the 75th percentile. Evaluate mobile and desktop separately; a good result for one device category does not establish a good result for the other. Google’s Web Vitals guidance lists these thresholds.
| Metric | Good threshold | What it reflects |
|---|---|---|
| LCP | 2.5 seconds or less | How quickly the main visible content loads |
| INP | 200 milliseconds or less | Responsiveness to user interactions |
| CLS | 0.1 or less | Visual stability as the page loads and changes |
INP replaced First Input Delay (FID) as a Core Web Vital in March 2024. Google’s announcement reported that 93% of sites had good mobile FID and 65% had good mobile INP at that time; these are historical figures from the 2024 announcement, not current estimates. Read the announcement.
Rank #2
- 5-in-1 USB-C Hub: Experience comprehensive connectivity featuring a Power Delivery input, two USB-A 2.0 ports, a USB-A 3.0 port, and an HDMI port. (Note: The USB-C power delivery input port is only for connecting an external wall charger to power your laptop and cannot power peripheral devices.)
- 90W Pass-Through Charging: Achieve optimal charging with 90W pass-through power to your laptop, supported by a total input of 100W, with the hub reserving 10W for operational efficiency. (Note: Wall charger not included.)
- Quick Data Transfers: Accelerate your productivity with rapid data transfers using a high-speed 5Gbps USB 3.0 port and two 480Mbps USB 2.0 ports.
- 4K HDMI Display: Enhance your visual experience with a hub capable of delivering 4K resolution at 30Hz in both mirror and extend modes. Please note that this hub is compatible with MacBook (macOS 12 and newer), Windows 10 and 11, ChromeOS, and laptops equipped with DP Alt Mode and Power Delivery. Note: This device is not compatible with Linux.
- What You Get: Anker USB-C Hub (5-in-1, 4K HDMI), welcome guide, 18-month warranty, and our friendly customer service.
How to measure an experiment’s effect
- Record the experiment assignment on the server. Attach the group or experiment version to your analytics or real-user monitoring (RUM) observations. Google recommends server-side group assignment and cautions against client-side tools that block rendering. Google’s business-impact guidance.
- Compare control and treatment among real users. Compare LCP, INP, and CLS by group, and segment results by relevant device categories such as mobile and desktop. Use the 75th percentile for each category rather than relying on a single average.
- Use lab tests to investigate, not to represent every visitor. Lighthouse can help catch regressions and investigate likely causes, but a single run cannot reproduce all devices, networks, caching conditions, interactions, or layout changes later in a page session. Conventional runs without interactions cannot directly measure INP. Lighthouse user flows can script interactions, but still complement field data rather than replace it. See Google’s explanation of lab and field data and Lighthouse user flows.
- Use field tools at the right level of detail. CrUX and Google’s Core Web Vitals tools help assess field performance. CrUX does not provide the per-pageview detail often needed to diagnose an experiment quickly; site-owned RUM can provide more detailed experiment-level observations. Google’s guidance.
Reduce the performance risk of an A/B test
- Prefer server-side assignment when it fits your implementation, so the browser does not have to wait for client-side variant selection before showing the page.
- Limit the experiment to pages where it is relevant and to a subset of users when practical.
- For layout-changing variants, account for the space new content will occupy to avoid pushing other content around.
- Keep a test only as long as needed, then remove its code or configuration after it ends.
- Validate changes with lab diagnostics, then monitor field results by experiment group and device category.
Google’s business guidance sums up the trade-off: “A/B testing can provide invaluable feedback before launching new changes, but the cost to page performance must be weighed up against any potential benefits they bring.” Google web.dev business-impact guidance.
Quick Recap
Best Value
- 5-in-1 Connectivity: Equipped with a 4K HDMI port, a 5 Gbps USB-C data port, two 5 Gbps USB-A ports, and a USB C 100W PD-IN port. Note: The USB C 100W PD-IN port supports only charging and does not support data transfer devices such as headphones or speakers.
- Powerful Pass-Through Charging: Supports up to 85W pass-through charging so you can power up your laptop while you use the hub. Note: Pass-through charging requires a charger (not included). Note: To achieve full power for iPad, we recommend using a 45W wall charger.
- Transfer Files in Seconds: Move files to and from your laptop at speeds of up to 5 Gbps via the USB-C and USB-A data ports. Note: The USB C 5Gbps Data port does not support video output.
- HD Display: Connect to the HDMI port to stream or mirror content to an external monitor in resolutions of up to 4K@30Hz. Note: The USB-C ports do not support video output.
- What You Get: Anker 332 USB-C Hub (5-in-1), welcome guide, our worry-free 18-month warranty, and friendly customer service.
Rank #4
- Dual Converters, Infinite Potential：Includes 2× USB C male to USB A female adapters and 2× USB A male to USB C female adapters. Perfect for a wide range of uses—tablets with Bluetooth keyboards, expand USB ports on macbook, and more. Two different converters for all your daily needs
- Next-Level 10Gbps & 3A Charging: No more slow 480Mbps, this usb to usb c adapter has a transfer speed of up to 10Gbps, allowing you to do more transferring in less time. This usb adapter fits both USB A and USB C charger, supporting up to 3A fast charging
- Upgraded Exquisite Craftsmanship: With an aluminum alloy housing and metal connector, the usbc to usb adapter is extremely durable and sturdy. Rigorously tested to withstand more than 10,000 times of plugging and unplugging, ensuring long-lasting performance
- Broad Compatible: The usb c to usb adapter widely supports all USB C/ USB A devices like laptops, tablets, cellphones, car chargers, and phone chargers. Such as compatible with MacBook Pro/Air 2023/2022, Thunderbolt 4/3 Devices,Apple MagSafe Watch 9/8/7/SE/Ultra, iPad Pro 2022/2021, Samsung Galaxy S23/S20/S10, and iPhone 17/16/15 Pro. Plug and play
- Please Note: To reach 10Gbps speed, keep the cable under 3.3 ft. For USB A Male to USB C adapters, try flipping the USB C connector. USB C Male to USB A adapters support bidirectional 10Gbps transfer within 3.3 ft
Rank #3
- Sleek 7-in-1 USB-C Hub: Features an HDMI port, two USB-A 3.0 ports, and a USB-C data port, each providing 5Gbps transfer speeds. It also includes a USB-C PD input port for charging up to 100W and dual SD and TF card slots, all in a compact design.
- Flawless 4K@60Hz Video with HDMI: Delivers exceptional clarity and smoothness with its 4K@60Hz HDMI port, making it ideal for high-definition presentations and entertainment. (Note: Only the HDMI port supports video projection; the USB-C port is for data transfer only.)
- Double Up on Efficiency: The two USB-A 3.0 ports and a USB-C port support a fast 5Gbps data rate, significantly boosting your transfer speeds and improving productivity.
- Fast and Reliable 85W Charging: Offers high-capacity, speedy charging for laptops up to 85W, so you spend less time tethered to an outlet and more time being productive.
- What You Get: Anker USB-C Hub (7-in-1), welcome guide, 18-month warranty, and our friendly customer service.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
