Explainer

https://github.com/explainers-by-googlers/declarative-performance-observer

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/explainers-by-googlers/declarative-performance-observer
• Primary contacts:
  • Shunya Shishido (@sisidovski), Google, Proposer / Implementer
• Organization/project driving the design: Google
• This work is being funded by: Google
• Incubation and standards groups that have discussed the design:
  • WICG: https://github.com/WICG/proposals/issues/280
  • Web Performance Working Group: Presented and discussed on June 18, 2026 (Minutes: https://w3c.github.io/web-performance/meetings/2026/2026-06-18/index.html)
• Standards group(s) that you expect to discuss and/or adopt this work when it's ready: W3C Web Performance Working Group

Feedback so far

• Multi-stakeholder feedback:
  • Chromium comments: Positive (proposer). The Chrome Loading team is actively implementing and experimenting with this feature in chromium (Origin Trial in M151–M155, tracking bug: https://crbug.com/505208781, ChromeStatus: https://chromestatus.com/feature/6594955352080384).
  • Mozilla comments: https://github.com/mozilla/standards-positions/issues/1458
  • WebKit comments: https://github.com/WebKit/standards-positions/issues/725
• Major unresolved issues with or opposition to this design:
  • No formal opposition has been expressed.
  • Active design discussions on GitHub include:
    • Custom metadata / dimensions (Issue #8): Exploring how developers can safely attach custom application dimensions.
    • Long-lived SPA documents (Issue #7): How to best support same-document transitions / Soft Navigations alongside terminal lifecycle report emission.

You should also know that...

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