If your experiment preview opens but you don’t see the expected change, follow the steps below to diagnose the issue.
Important: If the Mida pixel is not detected on the page, the preview will not run correctly.
Make sure the pixel is installed and loading on the page before attempting to preview an experiment.
1. Confirm the preview URL parameters
When you click Preview, Mida opens the page in a new window and appends preview parameters to the URL, for example:
?test-preview=12345&test-variant=Variant_1
What to check:
The page opens in a new tab or window
The URL contains both parameters
The parameters are not removed by redirects, cookie consent tools, or URL rewrites
If these parameters are missing or stripped, the preview may not run correctly.
2. Double-check page targeting rules
Preview mode still respects your experiment’s targeting rules.
Verify in your experiment settings that:
The Page URL rules match the previewed page
The rule logic is correct (e.g. contains vs equals)
There are no additional conditions preventing eligibility
If the page does not match the targeting rules, the preview may load but the change may not be applied.
3. Inspect the browser console for QA debug logs
Mida provides QA debugging information directly in the browser console.
How to check:
Right-click on the page
Select Inspect
Open the Console tab
The console logs can indicate:
Whether the preview is running
Whether the experiment was evaluated
Why a change may not have applied (e.g. targeting rules not matched, element not found)
This is the fastest way to understand why a preview didn’t show.
4. Common reasons the preview may not show the change
i) Pixel not installed or not detected
If the Mida pixel is missing, blocked, or not loading on the page, the preview will not run correctly.
Make sure:
The pixel script is present on the page
It loads without errors
It runs on the same domain and environment you are previewing
ii) Page targeting rules not matched
The preview URL loads, but the page does not meet the experiment’s targeting criteria.
iii) URL parameters removed or modified
Redirects, consent managers, or client-side routing may remove or change the preview parameters before the experiment evaluates.
iv) Timing mismatch (element not found)
The preview may not show the change if the element you’re trying to modify is not present in the DOM when the experiment runs.
This commonly happens when:
The element loads asynchronously (e.g. React, Vue, SPA navigation)
The element appears after a delay
The element only exists after user interaction (scroll, click, modal open)
In this case, the preview may still be running, but the change is skipped because the element could not be found at execution time.
How to confirm:
Open the browser Console
Review the Mida QA logs for messages indicating the experiment ran but the element was not found
How to fix:
Use a more reliable selector
Apply the change after the element appears
Ensure the change runs on the correct page or page state
Additional conditions not met
Audience rules, device targeting, or other conditions may prevent the change from applying, even though the preview link opens successfully.
Still not working?
If you’ve checked all the steps above and the preview still isn’t showing the change:
Copy the browser console logs
Share the preview URL
Contact support so we can help investigate further