Aug 8, 2025 | RUMCG Meeting

Attendees

Discussion on Chrome Soft Navigation API highlights its availability in August 2025, with performance observer entries for better interaction tracking; feedback requested from the community.
Noted challenges in aligning manual instrumentation with Chrome's automatic detection, suggesting portable JavaScript APIs for navigation start/end points.
Proposal of separate tracking for largest image and text LCP candidates to enhance debugging insights compared to Firefox's single frame reporting.
Cloudflare's default provision of server timing headers aims to improve tracking of prefetch and prerender requests; discussion on a future "CDN Day" for standardization.
In-person meetup planned at Amsterdam Google offices prior to Performance Now 2025 conference, featuring informal networking and food sponsorship.
Technical discussions on DOM modification thresholds and the use of Request Idle Callback for context tracking during soft navigation detection.
Questions raised regarding separate ICP callbacks; need for testing new metrics without disturbance to established workflows emphasized.
Community feedback urged on the Chrome Soft Navigation trial, particularly regarding false positives/negatives during initial testing phases.
Next community meeting scheduled for September 12th; Isaac will present on unresponsive crash reports during that session.
Insights into measurement differences reinforce the value of multiple candidates in LCP timing to address layout changes effectively.

Opening & Logistics (00:33 - 07:16)

Meeting logistics discussed, with challenges noted for Friday afternoon timing.
Next meeting scheduled for September 12th, approximately one month from now.
Isaac unable to attend to present on unresponsive crash reports and self-profiling API.

Chrome Soft Navigation Origin Trial Updates (12:01 - 19:07)

Chrome Soft Navigation API available in Chrome 139 origin trial since early August 2025.
API emits Interaction Contentful Paint performance observer entries instead of resetting LCP for soft navigations.
Different performance entries now include navigation IDs for better attribution across soft navigations.
Soft navigation detection requires user interaction, URL change, DOM modification, paint update, and history change.
Gilberto Cocchi and Michael Mocny seeking community feedback on API during origin trial.

Technical Implementation Questions (20:48 - 38:08)

Discussion on DOM modification thresholds for soft navigation detection.
Request Idle Callback and other scheduling mechanisms supported for maintaining context tracking.
Questions raised about separate ICP callbacks to test new metrics without disrupting existing workflows.

RUM Vendor Alignment Challenges (24:45 - 30:31)

Challenges aligning manual customer instrumentation with Chrome's automatic detection across browsers.
Suggestion for portable JavaScript APIs for declaring navigation start/end points.
Approach to measure differences between manual and automatic detection methods during transition.

Performance Now 2025 Meetup Planning (40:57 - 42:42)

In-person meetup offered at Amsterdam Google offices before Performance Now 2025 conference.
Security registration required, food sponsorship offered by Cliff Crocker and Karlijn Lowik.
Informal mixer format with potential announcements, pizza, and drinks.

LCP Measurement Differences (45:01 - 50:55)

Firefox reports all LCP candidates in a single animation frame while Chrome only reports the largest.
Multiple candidates useful for debugging layout changes affecting LCP timing.
Suggestion for separate tracking of largest image and text candidates for better insights.

️ Server Timing Updates (53:33 - 58:31)

Cloudflare now provides server timing headers by default for RUM customers.
Server timing headers added to track prefetch and prerendered requests as part of Speculation Rules.
Proposal for future "CDN Day" to discuss standardization and feature requests across CDN providers.

Isaac

Reschedule presentation on unresponsive crash reports and self-profiling API for September meeting (05:41)

Cliff Crocker

Set up Performance Now 2025 meetup logistics including venue booking and security registration process (42:42)

Karlijn Lowik

Set up Performance Now 2025 meetup logistics including venue booking and security registration process (42:42)

Community Members

Test Chrome Soft Navigation Origin Trial and provide feedback on false positives/negatives (17:09)
File bug reports with "soft nav" label in Chromium issue tracker for any problems encountered (19:07)

Meeting Organizers

Add LCP measurement differences discussion to September meeting agenda (51:52)
Consider server timing trailers discussion for future meeting agenda (57:14)
Evaluate CDN standardization discussion format and topics for potential future meeting (58:31)