no-duplicate-keyframe-selectors

Disallow duplicate selectors within keyframe blocks.

Background

The @keyframes at-rule in CSS defines intermediate steps in an animation sequence. Each keyframe selector (like 0%, 50%, 100%, from, or to) represents a point in the animation timeline and contains styles to apply at that point.

@keyframes test {
	0% {
		opacity: 0;
	}

	100% {
		opacity: 1;
	}
}

If a selector is repeated within the same @keyframes block, the last declaration wins, potentially causing unintentional overrides or confusion.

Rule Details

This rule warns when it finds a keyframe block that contains duplicate selectors.

Examples of incorrect code for this rule:

/* eslint css/no-duplicate-keyframe-selectors: "error" */

@keyframes test {
	0% {
		opacity: 0;
	}

	0% {
		opacity: 1;
	}
}

@keyframes test {
	from {
		opacity: 0;
	}

	from {
		opacity: 1;
	}
}

@keyframes test {
	from {
		opacity: 0;
	}

	to {
		opacity: 0.5;
	}

	to {
		opacity: 1;
	}
}

Examples of correct code for this rule:

/* eslint css/no-duplicate-keyframe-selectors: "error" */

@keyframes test {
	0% {
		opacity: 0;
	}

	100% {
		opacity: 1;
	}
}

@keyframes test {
	from {
		opacity: 0;
	}

	to {
		opacity: 1;
	}
}

When Not to Use It

If you aren't concerned with duplicate selectors within keyframe blocks, you can safely disable this rule.

Prior Art

• keyframe-block-no-duplicate-selectors