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

What is it?

Wraith uses either PhantomJS or SlimerJS to create screen-shots of different environments and then creates a diff of the two images, the affected areas are highlighted in blue

Photo of BBC News with a


To read our detailed instructions for setup and install, as well as example configs, visit wraith docs


Open terminal and run

gem install wraith

You can then run the following to create a template snap.js and config file:

wraith setup

Alternatively you can clone the repo.

git clone https://github.com/BBC-News/wraith
cd wraith
bundle install    

Using Wraith

You can type wraith into terminal to bring up the list of commands, but the one to start Wraith is

wraith capture config_name

This assumes that your snap.js and config.yaml are in the folders that were created on setup. There are other commands also available, these all expect a config_name to be passed as an option.

  wraith capture config_name  # A full Wraith job
  wraith compare_images       # compares images to generate diffs
  wraith crop_images          # crops images to the same height
  wraith folders              # create folders for images
  wraith generate_gallery     # create page for viewing images
  wraith generate_thumbnails  # create thumbnails for gallery
  wraith reset_shots          # removes all the files in the shots folder
  wraith save_images          # captures screenshots
  wraith setup                # creates config folder and default config


After each screenshot is captured, the compare task will run, this will output a diff.png and a data.txt. The data.txt for each file will show the number of pixels that have changed. There is a main data.txt which is in the root of the output folder that will combine all of these values to easier view all the pixel changes.


A gallery is available to view each of the images and the respective diff images located in the shots folder once all the images have been compared.


If you want to add functionality to this project, pull requests are welcome.

  • Create a branch based off master and do all of your changes with in it.
  • If you have to pause to add a 'and' anywhere in the title, it should be two pull requests.
  • Make commits of logical units and describe them properly
  • Check for unnecessary whitespace with git diff --check before committing.
  • If possible, submit tests to your patch / new feature so it can be tested easily.
  • Assure nothing is broken by running all the test
  • Please ensure that it complies with coding standards.

Please raise any issues with this project as a GitHub issue.

 Changelog - updated 2014-02-09

We have released Wraith as a Ruby Gem!! There is a new CLI to better interact with Wraith and it's commands.


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