An AET file generally refers to an After Effects master template, functioning as a reusable starter setup similar to an AEP but meant to be opened repeatedly without overwriting the original, so After Effects treats it like a master you open and then save as a new project, containing the full "recipe" for the animation—comps, timelines, layer stacks, keyframes, effects, expressions, cameras/lights, render settings, and organizational elements like folders and interpretations.
An AET typically doesn’t embed the raw media; instead it references external clips, graphics, and audio, which is why these templates are usually distributed as a ZIP with a Footage/assets directory and why After Effects may prompt for missing files if anything was moved, and because AETs may rely on specific fonts or third-party plugins, opening one on a new computer can lead to missing-effect notices until the
required items are added, while remembering that file extensions aren’t exclusive, so the safest way to confirm the correct app is checking "Opens with" or considering where the file originated.
An AEP file represents the editable project you’re actively working on, while an AET is a reusable template, so in practice the difference lies in purpose: you open an AEP to continue that same project, but you open an AET to create a new copy so the original stays clean.
That’s why AET formats are widely shared in motion-graphics template sets like intros, lower-thirds, and slideshows: the AET remains the creator’s master, and for each new video you open it, Save As a new AEP, then swap in your own text, media, logos, and colors, and even though both formats store the same project components—comps, layers, keyframes, effects, expressions, cameras/lights, and settings—and both usually reference external files, the AET safeguards the layout while the AEP becomes the editable end-user project.
Here's more information regarding
AET format review our web-page. An AET file retains the structure and animation logic of an After Effects project but not always the media assets, containing compositions with defined resolution, FPS, duration, and nesting, plus the complete layer arrangement—text, shapes, solids, adjustments, precomps, and placeholders—with layer properties like position, scale, rotation, opacity, masks, mattes, blending modes, parenting, and the project’s animation data including keyframes, easing, markers, and any expressions used to automate motion.
On top of that, the template stores all effects and their settings—color correction, blurs, glows, distortions, transitions, and more—along with any 3D setup such as cameras, lights, 3D layer properties, and render/preview settings, plus project-level organization like folders, label colors, interpretation rules, and sometimes proxies, but it typically does not bundle full footage, images, audio, fonts, or plugins, instead keeping links and dependencies that may trigger missing-asset or missing-plugin warnings on another computer until everything is relinked or installed.