Squash & Stretch is a smart keyframe assistant extension for Adobe After Effects from Mamoworld, and comes in a Free version and a $99 Pro version. It enables you to save time animating with numerous ready-to-use behaviors, handcrafted by pros and controlled intelligently so your animations can come to life without starting from scratch each time. Squash & Stretch creates simple keyframes not expressions, so it’s fast and easy to modify animations once you understand the toolset.

In case you’re newer, Squash & Stretch is just one of the essential 12 principles of animation, a set of principles explained in depth by “old men” Disney animators Ollie Johnston and Frank Thomas in their 1981 book The Illusion of Life: Disney Animation.

If you don’t have Pixar director John Lasseter’s seminal 1987 SIGGRAPH paper based on The Illusion of Life, there’s a decent scanned copy available: “Principles of Traditional Animation Applied to 3D Computer Animation.” There’s also a ton of explanatory videos out there (School of Motion for example), but a looping gif on Tumblr has all twelve principle on one page.

Installation of this keyframe assistant was a bit confusing at first, since this After Effects Extension uses the ZXP Installer from
aescripts.com. In any case, installation ended up being a breeze. Once After Effects is started, you’ll find the tool under Window > Extension.

With Squash & Stretch you get 10 behaviors Free, or 61 behaviors in the Pro version, the latter extendible with extra bundles. Squash & Stretch behaviors not only move and deform a layer but also come with a variety of built-in sound designs for maximum impact — 91 Free and 350 in the Pro version. You’ll just need select a pre-matched sound in a pop-up, and it’ll be inserted into your composition when you apply the behavior. Of course, you can also use the sounds independently of Squash & Stretch. Here’s an overview video:

Squash & Stretch features some intuitive slider controls to make elements jump higher and squish weaker or stronger. Parameter and keyframe control is featured in these videos from Mamoworld.

Using a simple square solid or text is an easy way to begin experimentation since that matches the previews. I didn’t find the tools entirely intuitive at first, especially where in the timeline to Apply the effects, so unless you’re an advanced user you might look at the mini-tutorials. They’re very short and to the point, so you can get through the bunch in little time, then be on your way. Toolset features with mini-tutorials include a Precompose tool, a Text Splitter (Pro version), a Shift Position tool for auto-positioning, a Transitions tool, sound effects, and a Layer Stagger tool. 

Boone Loves Video already has his own video overview too: