3 min read performance

The Emergence of the Long Animation Frames API

This article delves into the Chrome team's proposal for the Long Animation Frames API (LoAF), a tool aimed at enhancing UI responsiveness and complementing the Interaction to Next Paint (INP) Core Web Vital.

Enhancing Web Performance: The Emergence of the Long Animation Frames API

In the dynamic world of web development, the Chrome team’s proposal for the Long Animation Frames API (LoAF) marks a significant stride in understanding and improving user interface (UI) responsiveness. This innovative API targets the shortcomings of the Long Tasks API and aligns with the Interaction to Next Paint (INP) Core Web Vital, which is pivotal in measuring web responsiveness.

From Long Tasks to Long Animation Frames

The Long Tasks API, established since Chrome 58, has been instrumental in identifying tasks that keep the main thread busy for over 50 milliseconds. However, its utility in Real User Monitoring (RUM) has been limited due to its basic attribution model and lack of detailed insights into the tasks’ origins and impacts.

Addressing the Gaps with LoAF

LoAF steps in to fill these gaps. Unlike its predecessor, which focuses on individual tasks, LoAF shifts the focus to long animation frames, offering a holistic view of what’s happening during rendering updates.

Comprehensive Analysis

LoAF’s approach encompasses all tasks within an animation frame, providing a more complete picture of the factors delaying rendering. This frame-based analysis is crucial for a deeper understanding of web performance issues.

Enhanced Detailing

One of the significant advancements of LoAF is its detailed breakdown of frame durations, including render start, style, and layout calculations. This granularity enables developers to pinpoint and address specific performance bottlenecks.

Improved Script Attribution

LoAF goes beyond just identifying long tasks. It attributes each script contributing to a long animation frame, detailing script names, types, and execution specifics. This level of detail is invaluable for developers looking to optimize web performance.

Implementing the LoAF API

Available as an origin trial from Chrome 116, LoAF can be enabled via Chrome flags. Its real-world application is particularly beneficial, as it provides contextual data that lab tools like Lighthouse might miss.

Strategies for Effective Use

Developers can employ various strategies to leverage LoAF, such as monitoring all long animation frames, analyzing data patterns, and correlating LoAF data with INP interactions. This helps in identifying and rectifying user experience issues more efficiently.

The Future of Web Performance Tools

LoAF’s potential integration into tools like Lighthouse and Chrome DevTools could revolutionize how developers approach performance optimization. By offering detailed performance data, these tools can aid developers in pinpointing and resolving specific UI responsiveness issues.


The Long Animation Frames API is a game-changer in the realm of web performance. By providing a more nuanced understanding of long animation frames and their impact on UI responsiveness, LoAF empowers developers to create smoother, more responsive web experiences. As it evolves, its role in enhancing web performance and user satisfaction is expected to be significant.

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