Skip to content
Switch branches/tags

Wraith logo

build status rubygems version codeclimate report

Wraith is a screenshot comparison tool, created by developers at BBC News.

DocumentationSourceResponsive News Website

What is it?

Wraith uses a headless browser to create screenshots of webpages on different environments (or at different moments in time) and then creates a diff of the two images; the affected areas are highlighted in blue.

Photo of BBC News with a diff


For instructions on how to install, set up and use Wraith and all of its features, visit the Wraith documentation.

A brief overview of how Wraith works is provided below.

Wraith modes

There are several ways in which Wraith can be used:

  1. Comparison of 2 domains (wraith capture). There are also some specialist options within this mode:
    • Spidering 2 domains for changes (wraith capture when no paths property is provided in the configuration file)
    • Running several comparisons at once (wraith multi_capture)
  2. Comparing the same domain over time (wraith history, then wraith latest)

Whichever mode you decide to run Wraith in, the process it follows is generally the same:

  • takes screenshots of your webpages
  • runs a comparison task across them
  • outputs a diff PNG file comparing the two images, and a data.txt file which contains the percentage of pixels that have changed
  • packages all of this up into a gallery.html, ready for you to view
  • if any screenshot's diff is above the threshold you specified in your configuration file, the task exits with a system error code (useful for CI)
  • the failed screenshot will also be highlighted in the gallery


ImageMagick is required to compare the screenshots and crop images.

Wraith also requires at least one of these headless browsers:

  • PhantomJS
  • CasperJS (which can be used to target specific selectors)
  • SlimerJS
  • Chrome (Currently using Selenium WebDriver + Chromedriver for Chrome; Can target specific selectors)


Please read how to contribute to Wraith.


Wraith is available to everyone under the terms of the Apache 2.0 open source license. Take a look at Wraith's LICENSE file.



Anyone interested in integrating selenium capability with Wraith should check out Selenium-Wraith (maintained by Mathew Hall), which was forked from BBC's Wraith on 16/04/14 and adds the following capabilities:

  1. Selenium integration, both running locally on a desktop or on a selenium grid
  2. Browser to browser screenshot comparison
  3. Page component-based comparison