The will-change property in CSS signals the browser that an element is about to change, allowing it to optimize rendering. 1. It informs the browser which properties will change, such as transform, opacity, scroll-position, or contents. 2. The browser may then promote the element to its own layer, pre-allocate resources, and avoid costly re-optimizations. 3. Use it selectively—before changes occur (e.g., on hover) and remove it afterward—to avoid unnecessary resource consumption. 4. Unlike older hacks like translateZ(0) or opacity: 0.99, will-change provides a more intentional and efficient way to prepare for visual changes without forcing layers unnecessarily.

The will-change property in CSS is a hint to the browser that an element is expected to change, which can help improve performance by allowing the browser to optimize how it handles rendering and compositing before the actual changes happen.

What does will-change actually do?

Browsers are pretty good at optimizing rendering on their own. However, sometimes they don’t know ahead of time what’s going to change — especially when those changes are triggered by user interaction or JavaScript. That’s where will-change comes in.

By using will-change, you're telling the browser: "Hey, I’m about to animate or modify this element in some way — get ready." In response, the browser might take steps like promoting the element to its own layer, pre-allocating resources, or avoiding certain optimizations that would be expensive to undo later.

Common values include:

• will-change: transform;
• will-change: opacity;
• will-change: scroll-position;
• will-change: contents;

Each tells the browser what kind of change is coming, so it can prepare accordingly.

When should you use will-change?

It’s most useful when you know something will change soon — for example, during hover effects, transitions, or animations. A common use case might be:

.button:hover {
  will-change: transform;
}

This helps the browser prepare for a transform-based animation (like a scale-up on hover) before it actually starts happening.

However, don’t overuse it. If you apply will-change to too many elements or for properties that rarely change, you could end up hurting performance instead of helping it. Creating layers and prepping for changes uses memory and processing power, so it's best reserved for elements that genuinely benefit from the optimization.

Some general guidelines:

• Use it only when you notice jank or lag in animations.
• Apply it just before the change happens (e.g., on hover or focus), not too early.
• Remove it once the change is done if the element won’t be changing again soon.

How is it different from translateZ(0) or opacity: 0.99?

You may have seen people using tricks like transform: translateZ(0) or opacity: 0.99 to force hardware acceleration. These work by triggering the creation of a new compositor layer, similar to what will-change might do — but with a key difference: those hacks are blunt instruments.

They force layer creation regardless of whether it's needed, and can lead to excessive memory usage or slower rendering due to too many layers. will-change, on the other hand, gives a more intentional signal to the browser, allowing it to make smarter decisions.

Still, both approaches are about preparing the browser for upcoming visual changes. The difference is that will-change is designed specifically for this purpose and is more future-proof as browsers evolve.

Used wisely, will-change can smooth out animations and interactions without much effort. But like any performance tool, it works best when applied selectively and thoughtfully.

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