Knowledge
How Spark Speed checks itself
Most cache plugins make assumptions and hope for the best. Spark Speed renders every page in the shadow and compares the result, so an optimization only stays in place if the page still looks exactly the same.
In a nutshell
- Every optimization is verified per page
- A shadow render compares before and after
- Any change that produces a difference is not applied
What a shadow render is
Before Spark rolls out an optimization, it creates a second, hidden render of the same page with the change applied. That shadow version is compared to the original for layout, color, and text.
What happens when there's a difference
If Spark spots a deviation, like a shifted element or a changed font, the optimization won't be applied to that page. This prevents a speed gain from quietly breaking your design.
- No difference: the optimization stays
- Difference found: the change is rolled back
- The check runs per individual page, not all at once for the entire site
Good to know: because the check works per URL, you never need to disable everything or nothing. One problematic page won't affect the rest of your site.
See what changes on each page before you lock anything in.
Frequently asked questions
No. The shadow render happens in the background, not during the visit. Visitors only see the verified end result.
Then that page simply stays untouched and safe. The remaining pages still benefit from the optimization.
Yes, Spark tracks what has been applied per page, so you can always verify what happened.