For websites, there's a bunch of hosted services for this, like VisualPing or ChangeTower or Sken.io or BrowserStack. It's often called "visual regression testi

For websites, there's a bunch of hosted services for this, like VisualPing or ChangeTower or Sken.io or BrowserStack. It's often called "visual regression testing". You can also do this yourself with something like Playwright: https://playwright.dev/docs/test-snapshots https://playwright.dev/docs/test-snapshots For email templates, they usually create a HTML version hosted online somewhere too, don't they? You can probably use the same tools for those if they're publicly accessible.