Screenshot comparison tool used for CSS Visual Regression Testing.
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Latest commit 13b60ad Apr 5, 2016

Snap And Compare

SnapAndCompare is an easy to use screenshot comparison tool used for CSS Visual Regression Testing built using NodeJS.


It can compare against a single environment or dual and will produce visuals and equality stats on image comparisons.

Run in standalone mode or if you give a watchFile will run everytime that is updated/saved (useful for SASS development).


Master image


Download and install NodeJS

Download and install GraphicMagick (gm)

brew install graphicsmagick

Or if that doesn't work install from source (

sudo make install

Download app dependencies

npm install


Update the config.js file to hold the masterUrl and diffUrl you need (they are often the same but not always) Run (first builds initial snapshot, second builds diff and compares):

node snapandcompare.js
node snapandcompare.js

How does the logic work:

Without a watchFile:

First run : For all Breakpoints will check if a master image exists, if not will create one.

Second run: For all Breakpoints will find the master image, create a new .diff image and run a comparison on the two producing a .fail image and flagging up if the images differ.

After that: For each Breakpoint it will either compare against the diff or download a new Master image (depending on what already exists in /screenshots).

With a watchFile:

It will continually run on save of the file. It will flag up the status of each Breakpoint as PASS or FAIL.

First run: On save of watchFile it will create the Master files after that will run the comparison evertime it detects a change.


  • Swap the config files and run the program to test. ('./config') for ('./config.test').