Screenshot checks, with a limit
Every StillWorks visit saves a picture of the pages it opened. We compare that picture with the last visit. A big visual change is noted. It does not, by itself, mean the app is broken.
Why we do not fail on the picture alone
You might change a headline on purpose. If we emailed you every time the pixels moved, the alerts would be noise. We email when a page fails to open, returns an error, or shows browser and network problems.
The dashboard still shows the pictures and the percent that changed, when we can compare them.
What the picture is
It is the browser window, not a full-page poster of the whole site. The first check has nothing to compare. Later checks compare the same step, such as Homepage, when the size matches.
Questions
Do you store the pictures?
Yes. Free-check pictures are on a public result page. Paid-app pictures stay in your account.