Caption vs Popup Window: Shopify Performance Comparison
Popup Window wins with Grade C vs Grade D — a one-grade performance difference that compounds on mobile devices.
Both apps provide popup, email capture, and conversion optimization functionality for Shopify stores. This page presents StackConflict’s independent lab results for both — measured in a clean-room environment with no other apps installed.
Head-to-Head Metrics
| Metric | Caption | Popup Window | Faster |
|---|---|---|---|
| Overall Grade | D | C | Popup Window |
| JS Payload | 517.67 KB | 326.89 KB | Popup Window |
| CPU Desktop | 76 ms | 90 ms | Caption |
| CPU Mobile | 127 ms | 425 ms | Caption |
| Layout Shift | 0.0 | 0.0 | Caption |
Mobile CPU measured with 4× CDP throttle (mid-range Android). Tested 2026-05-31.
Popup Window — The Faster Option (Grade C)
Popup Window scores Grade C with a JS payload of 326.89 KB and 90 ms desktop CPU execution. Mobile CPU: 425 ms. Even as the faster of the two options, merchants on mobile-heavy stores should weigh its impact on their combined app stack.
View full Popup Window speed report →
Caption — The Heavier Option (Grade D)
Caption scores Grade D with a JS payload of 517.67 KB and 76 ms desktop CPU execution. Mobile CPU: 127 ms. This places it in the heavier half of StackConflict’s benchmark dataset — merchants running mobile-first stores should evaluate whether the feature value justifies the performance tradeoff.
View full Caption speed report →
When to Choose Caption
- Its unique feature set has no lighter equivalent in StackConflict’s database
- Your store traffic is predominantly desktop
- You have already removed or lightened other heavy scripts to compensate
When to Choose Popup Window
- Its unique feature set has no lighter equivalent in StackConflict’s database
- Your store traffic is predominantly desktop
- You have already removed or lightened other heavy scripts to compensate
Performance Verdict
Winner: Popup Window — Popup Window wins with Grade C vs Grade D — a one-grade performance difference that compounds on mobile devices.
Both apps carry Grade C — see StackConflict’s full Popups rankings for lighter alternatives.
About This Test
StackConflict measures each Shopify app in an isolated clean-room environment — a single development store, no other scripts, Playwright-controlled browser. V8 CPU cost is the ScriptDuration delta before and after injection. CLS is captured from the same browser session. Results represent the median of three independent runs with outliers removed.
Data from the StackConflict Lab. Last updated 2026-05-31.