DiffCop is an automated visual diff tool that sends you e-mail alerts for any visual changes to your site after deploys. We use phantomjs to take screenshots of different versions of your site, and process the most recent screenshots to highlight any regressions. That lets you see, at a glance, whether anything broke—without having to write tons of tests for each thing.

We decided to pursue this idea after polling several YC founders about this versus our other idea—"feature flags as a service"—and hearing them light up at the diff idea and actually agree to use this once available.

We decided to focus on two dead-simple use cases:

  1. Sign up with a list of URLs and email, and we email you the diffs
  2. Alternatively, Heroku users can paste just one line into their terminal to get an email after each deploy

The key to being able to grok the diffs is our highlight view. It makes the "where's waldo" of finding regressions much easier. It's like cheating.

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