Wraith — A responsive screenshot comparison tool
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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 diff


You'll need either PhantomJS or SlimerJS, ImageMagick & Ruby 1.9.3 or greater. It's up to you to decide which browser engine you want to run it against.


On Mac OS X, the best way to install dependencies is if you have homebrew. It is the quickest way to install PhantomJS & ImageMagick.

brew install imagemagick
brew install phantomjs or brew install slimerjs


On Windows it's important to install ImageMagick from the binary found here. This will ensure that ImageMagick is listed first in your PATH.

To check your path after installing, open a command line window and type:


This will return a list of executables in you PATH separated by semi-colons ;

C:\Program Files\ImageMagick-6.8.7-Q16;C:\Windows\system32;C:\Windows...

If ImageMagick is in your path but not listed first you can edit your path by following the instructions here

If ImageMagick is not in your PATH at all but you have it installed you will need to add it in. Follow the instructions from the link above and add in the path to where you have ImageMagick installed. For example C:\Program Files\ImageMagick-6.8.7-Q16; Make sure the version number and location are correct for your system.


On Ubuntu 12.04, you will need to apt-get the following packages:

  • libicu-dev
  • imagemagick
  • rake

And then download the PhantomJS binary package from http://phantomjs.org/.


Open terminal and run

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

You can then run the following inside the Wraith directory:

bundle install

If you don't have bundler installed, install it :

gem install bundler

Alternatively you can download the install script via curl, this will not create a git repo though.

curl -fsSL https://raw.github.com/bbc-news/wraith/go/install | bash
cd wraith
bundle install    


All config options will be placed in config.yaml. You can specify the snap file name, this could be used in a situation where you have a large amount of config files. You can set the headless browser, domains of the 2 sites you are comparing, URL paths, screen widths & HTTP headers. If you don't want to set paths, you can use the spidering option to check your entire website. We use ImageMagick to process the images, we set a fuzz on the images to handle anti aliasing, this can be lowered or increased in the config.

# Headless browser option
  webkit: "phantomjs"
  # gecko: "slimerjs"

# Only used for webdriver
  base: firefox
  compare: firefox

# If you want to have multiple snapping files, set the file name here
snap_file: "snap.js"

# Type the name of the directory that shots will be stored in
  - 'shots'

# Add only 2 domains, key will act as a label
  english: "http://www.live.bbc.co.uk/news"
  russian: "http://www.live.bbc.co.uk/russian"

#Type screen widths below, here are a couple of examples
  - 320
  - 600
  - 768
  - 1024
  - 1280

#Type page URL paths below, here are a couple of examples
  home: /
  uk_index: /uk

# If you don't want to name the paths explicitly you can use a yaml
# collection as follows, and names will be derived by replacing / with _
# paths:
#  - /imghp
#  - /maps

#Amount of fuzz ImageMagick will use 
fuzz: '20%' 

#Set the number of days to keep the site spider file
  - 10

You can also specify PhantomJS command line options in config.yaml.

For example to tell PhantomJS to ignore SSL errors:

phantomjs_options: "--ignore-ssl-errors=true"

Using Wraith

If you are new to ruby, rake and PhantomJS, here is a great screencast about how to use Wraith by Kevin Lamping

There are two ways of using Wraith, the fastest is to simply type rake.


You may want to deal with multiple config files so you can compare different pages, different sites or different viewports. In order to handle this, you can pass in a different config file by typing the following into terminal. The default is config.yaml, so even if you don't pass a file in, it will still run. If you have deleted config.yaml, make sure you are inside the configs directory before running the command.

rake config[config_name]

On Windows before running the rake command you will need to make a small edit to the wraith.rb file. Locate lines 60 and 70 and switch the commenting as described.

Real devices and browsers

If you want to run Wraith against Android and iOS browsers, as well as Firefox/Chrome, you can with WebDriver. By setting the device name to the correct driver, e.g Firefox, then running the WebDriver task, you have the option to see images from real browsers. This works well on real devices, so will enable realistic testing instead of headless. There is a short getting started guide here. In order to use WebDriver, you must use the WebDriver task

  rake webdriver


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 just want to see a single domains images and not compare them, perhaps for archiving, remove a domain and run the new rake task. For default config, use grab, or specify a config using grabber.

rake grab and rake grabber[config]


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.

Running Tests


## Changelog - updated 6/12/13 Merge pull request #64 from BBC-News/fuzz Merge pull request #63 from shuynh/add-nokogiri Merge pull request #57 from BBC-News/on_devices Merge pull request #61 from jaikdean/allow-numbers-in-domain-names Merge pull request #59 from lewisnyman/master Merge pull request #55 from BBC-News/gallery_fix Merge pull request #51 from boldfacedesign/master Merge pull request #53 from BBC-News/browser_option Merge pull request #50 from nikai3d/patch-1 Merge pull request #49 from boldfacedesign/master Merge pull request #44 from rupl/master Merge pull request #46 from BBC-News/different_snap_file Merge pull request #41 from BBC-News/new-config Merge pull request #40 from tiemevanveen/master Merge pull request #36 from thingsinjars/patch-1 Merge pull request #37 from thingsinjars/patch-2 Merge pull request #34 from malengrin/master Merge pull request #33 from hoguej/feature/point_directly_at_install_script Merge pull request #22 from doryphores/phantomjs_options Merge pull request #27 from reggieb/code_tidy Merge pull request #24 from hoguej/feature/unit_tests Merge pull request #21 from doryphores/sort_files_before_compare Merge pull request #13 from BBC-News/crop-images Merge pull request #18 from ecometrica/gallery Merge pull request #15 from timabell/move-data-file Merge pull request #14 from timabell/unnamed-paths Merge pull request #5 from BBC-News/typekit-fix Merge pull request #8 from jaredly/patch-1 Merge pull request #2 from Kami/fix_ruby_compatibility Merge pull request #1 from BBC-News/freedom


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.