Overview
When running A/B experiments through Heatmap.com, you rely on preview links to review your variant pages and analyze heatmap data without impacting live visitors. This article covers two common issues users run into:
Preview links that stop working after an experiment is ended
Previews that load but look broken — missing styles, images, or layout
Both are fixable. Here's everything you need to know.
Section 1: Why Did My Preview Links Stop Working?
What's happening?
Preview links use the ?ig-preview= URL parameter to load a specific experiment variant. This parameter needs an active, live experiment to hook into. The moment a test is ended, there's nothing for the parameter to connect to — so the link stops working.
This is by design, not a bug.
Why does it work this way?
The preview system is tied to the experiment's active state because it's pulling the correct variant configuration in real time. An ended experiment no longer has an active configuration to serve, so the preview has no source to load from.
Section 2: How to Keep Preview Links Working After You're Done Collecting Data
Pause the experiment instead of ending it
This is the recommended approach. Pausing an experiment stops all live traffic from being assigned to test variants — but it keeps everything else intact:
Your experiment configuration is preserved
Your preview links remain functional
Your heatmap data stays accessible
You can continue analyzing variant performance through the Chrome extension or Heatmap dashboard without affecting any real users.
To pause an experiment:
Go to your experiment in the dashboard
Click Pause (not End)
Your preview links will remain active immediately
End the experiment only when your analysis is fully complete and you no longer need access to the preview.
Section 3: My Test Is Already Ended — Can I Get My Preview Links Back?
Yes. You'll need to briefly resume the experiment, then pause it right away. This restores the active state that the ?ig-preview= parameter requires.
Steps to restore preview access:
Find the ended experiment in your dashboard
Click Resume — this reactivates the experiment briefly
Immediately click Pause to stop live traffic from running again
Your preview links will now work
Note: Between resuming and pausing, a small number of live visitors may temporarily be served the experiment variants. Pause as quickly as possible to minimize this.
Section 4: Quick Reference — End vs. Pause vs. Resume
Situation | Action |
Finished collecting data, still analyzing | Pause |
Analysis complete, no further access needed | End |
Test ended too early, need previews back | Resume → immediately Pause |
Want to run the test again from scratch | Resume |
Section 5: My Preview Loads, But the Page Looks Broken
This is a separate but related issue. Sometimes a preview link works — the variant loads — but the page looks visually broken: missing CSS, unstyled elements, images not loading, or a layout that doesn't match what visitors actually see.
Why does this happen?
Heatmap's servers need to access your site's CSS and asset files to render the page accurately. If those files are blocked, the visual rendering will be incomplete or broken. Common causes include:
Geolocation blocking — your site restricts access to assets based on the visitor's region, and Heatmap's servers may be hitting that restriction
Domain or referrer blocking — your site only serves assets to requests from approved domains
Cookie or sessionStorage dependencies — some assets only load after a session has been initialized, which Heatmap's servers may not have
How to fix it
Option 1: Whitelist Heatmap's IP addresses Allow Heatmap's IP addresses in your server or CDN settings so our servers can fetch CSS and assets freely. See → Heatmap IP Addresses
Option 2: Allow Heatmap's domain/referrer Update your referrer-based access rules to allow requests originating from Heatmap's domain.
Option 3: Check your Cloudflare settings If you're using Cloudflare with Bot Fight Mode enabled, it may be blocking Heatmap's servers from fetching your assets. See → Cloudflare Bot Fight Mode and Heatmap
If the page still looks broken after trying these steps, contact our support team at support@heatmap.com with a description of the issue and the affected URL.
Section 6: Best Practices for Experiment Preview Management
Always pause before analyzing. Once you've called a test and stopped sending traffic, pause rather than end — you'll almost always want to go back and review the heatmap data.
Don't end a test until you're fully done. Reactivating an ended test to restore previews is possible, but it briefly re-exposes visitors to the experiment.
Keep preview links saved. Store your
?ig-preview=URLs in your experiment notes or documentation so your team can access them without hunting.Use IP Blocking when reviewing previews. If your team is reviewing variants and clicking around on preview links, those sessions will be tracked. Block your team's IP addresses to keep your heatmap data clean. See → How to Set Up IP Blocking
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Questions? Reach out to our support team at support@heatmap.com or start a conversation in the chat bubble on your dashboard.