How to Generate a CSS Animation

CSS animations bring interfaces to life — loading spinners, entrance effects, hover feedback, and attention-grabbing highlights all rely on them. But writing @keyframes rules and dialing in timing functions by hand means a lot of trial and error. The CSS animation generator gives you a visual timeline so you can design animations by seeing them rather than guessing at percentages.

Animation vs transition

CSS offers two mechanisms for motion, and choosing the right one matters. Transitions animate between two states when a property changes (like on hover). They are simple, implicit, and require a trigger. Animations use @keyframes to define an explicit sequence of states and can run automatically, loop infinitely, and move through multiple intermediate steps. Use a transition when you have a simple A-to-B state change. Use an animation when you need multi-step sequences, auto-playing effects, or looping motion.

Understanding keyframes and performance

A @keyframes rule defines named waypoints at percentage positions along the animation timeline. At 0% (or from) you set the starting state, at 100% (or to) the ending state, and you can add as many intermediate points as you need. The browser interpolates between these points using the easing function you specify.

Performance is the hidden cost of CSS animations. Animating transform and opacity is hardware-accelerated on most browsers because these properties can be composited on the GPU without triggering layout recalculations. Animating width, height, margin, padding, or top/left forces the browser to recalculate layout on every frame, which can cause visible jank — especially on mobile devices.

The will-change property hints to the browser that an element is about to animate, allowing it to promote the element to its own compositing layer ahead of time. Use it sparingly: will-change: transform on the element you are about to animate is helpful, but applying it to dozens of elements wastes memory.

Tips and best practices

• Stick to transform and opacity for smooth 60fps animation. Move elements with translateX() / translateY() instead of changing left / top. Scale with scale() instead of changing width / height.
• Use cubic-bezier() for custom easing. The built-in keywords (ease, ease-in-out) cover common cases, but a custom cubic-bezier curve lets you create bouncy, elastic, or snappy motion that feels more intentional.
• Respect prefers-reduced-motion. Wrap your animations in a @media (prefers-reduced-motion: no-preference) query so users who are sensitive to motion can opt out. This is both an accessibility requirement and a best practice.
• Keep animations short. Most UI animations should be 200-500ms. Anything longer feels sluggish; anything shorter feels invisible. Loading and attention animations can loop but should still use quick individual cycles.

Common issues

• Animation looks choppy on mobile. You are likely animating a layout property. Check the browser’s performance profiler for layout thrashing and switch to transform-based movement.
• Animation only plays once. The default animation-iteration-count is 1. Set it to infinite for looping animations, or to a specific number for repeated but finite effects.
• Element snaps back to original state after animation ends. By default, the element reverts to its pre-animation styles when the animation completes. Add animation-fill-mode: forwards to keep the element in its final keyframe state.