Inspect Element on steroids: study how things are made on the web in real-time and copy computed styles with no hassle (neither longhand styles)
CodeSandbox is an online editor that helps you create web applications, from prototype to deployment.
Keyframes gives you a visual timeline to help you create, view, and run animations without having to go back and forth between your browser and editor.
And it gives you the CSS when you're done.
Use the web app to create an animation on a basic shape, or install the extension to create an animation on any element, anywhere, on any website.
Contraste is a simple app for checking the accessibility of text against the Web Content Accessibility Guidelines (WCAG).