design-reviews#1224: Incubation: Lightweight and Conditional Tracing for long animation frame timing API

#1224: Incubation: Lightweight and Conditional Tracing for long animation frame timing API

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Opened

Apr 28, 2026

Explainer

https://github.com/MicrosoftEdge/MSEdgeExplainers/blob/main/ConditionalTracing/explainer-for-loaf.md

The explainer

Includes the information requested by the Explainer Explainer.
Follows the Web Platform Design Principles.
Includes or links to answers to the Security/Privacy Questionnaire.
Describes user research you did to validate the problem and/or design.

Where and by whom is the work is being done?

GitHub repo:https://github.com/w3c/long-animation-frames
Primary contacts:
- guohuideng@microsoft.com
Organization/project driving the design: Microsoft and Google
This work is being funded by: Microsoft and Google
Incubation and standards groups that have discussed the design:
- github discussion: https://github.com/w3c/long-animation-frames/issues/3
- WebPerf WG minutes: https://docs.google.com/document/d/1M56DC5CweAcMCNd3yc_eDRuDNmfwcx3CQLRTWoMG4AM/edit?tab=t.0#heading=h.bpywm5gwk0li
Standards group(s) that you expect to discuss and/or adopt this work when it's ready: WebPerfWG

Feedback so far

Multi-stakeholder feedback:
- Chromium comments: planning to prototype this and work with the WebPerfWG.
- Mozilla comments: TBD
- WebKit comments: TBD
Major unresolved issues with or opposition to this design: N/A

You should also know that...

No response

Track conversations at https://tag-github-bot.w3.org/gh/w3ctag/design-reviews/1224

Discussions

Discussed May 18, 2026 (See Github)

Lola: yesterday, we went through the issue triage. This issue, and the next, we couldn't find anyone to take on in Atlantic breakout. So we wanted to assign them from this breakout. Anyone?

The first is performance-based. It's looking at measuring the performance for animations.

Xiaocheng: I will look at this.

Discussed May 18, 2026 (See Github)

Jeffrey: I believe this will be in web-perf eventually, but it's currently in incubation.

Lola: Anyone want to take this? Hearing nothing, I can ask in Slack or in Eurasia tomorrow.

Discussed Jun 1, 2026 (See Github)

Jeffrey: Xiaocheng drafted a response https://github.com/w3ctag/design-reviews-private-brainstorming/issues/279#issuecomment-4542454000

Heather: I have no problem with the draft response. We are just making comments, not asking questions - would we close it or leave it open for them to respond.

Jeffrey: I think this is a good question for Xiaocheng because they didn't suggest whether it is "satisfied with concerns" or wanted to ask questions

Heather: Could we leave it open for a set period of time

Jeffrey: Or we could ask a question.. I see that Matthew had been involved in the previous approach - I would like to ask Matthew what he thinks - and otherwise say this breakout is happy with the reply.

Brian: That sounds reasonable.

Jeffrey: I have replied to the brainstorming issue - once they are happy they can just post.

Discussed Jun 8, 2026 (See Github)

Xiaocheng: I have a proposed comment in the thread.

Heather: I'm good with that comment. Any concerns?

Comment by @xiaochengh Jun 10, 2026 (See Github)

Hi @guohuideng2024, the TAG reviewed this and fount it much more plausible than the previous approach. The overall mechanism looks highly feasible to us.

We have some comments at a lower level regarding the API design.

The proposed new APIs markCondition() and measureConditional() are directly tied to long animation frames, and therefore:
- The connection between these APIs and LoAF is not clear from the names and may be confusing
- This is not extendable to use cases like, e.g., we want to analyze long tasks instead of long animation frames, or if there are new types of performance incidents we want to introduce in the future
We are also unsure why we need to introduce "conditional" marks and measures, instead of somehow allowing existing marks and measures to be attributed to LoAF and similar incidents.