Detect Wagtail 
Detect whether a site or page is built with Wagtail.
Usage
You can run the detection with:
- The online website, detect-wagtail.netlify.app.
- A bookmarket, also available from detect-wagtail.netlify.app.
- A browser extension thanks to Wappalyzer.
- A Node CLI, also thanks to Wappalyzer.
- As an npm package for more custom needs, detect-wagtail
How it works
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.