Is a site built with Wagtail? Let’s check.
The detection is based on Wagtail image renditions, so only works if the page contains user-uploaded images.
Do it yourself
The detection is also available as a bookmarklet, usable in any desktop browser. Simply drag the link below into your bookmarks bar and then click it to run the check on the current page.Wagtail?
Alternatively, you can also use Wappalyzer or WhatCMS.org.
How it works
Full read: Detecting Wagtail in the wild.
This uses regular expressions to check whether images on the page match a predetermined pattern. Here is a simplified diagram of the logic (created with regexper):
There can be false positives with such a simple check, but it has the benefit of working regardless of whether the target site is directly served by Wagtail, or if Wagtail is used as a headless CMS. For further info, view the implementation on GitHub.