Oct 10, 2025 | RUMCG Meeting

Attendees

• Cliff Crocker
• Nic Jansma
• Robin Marx
• Andrew Creskey
• Barry Pollard
• Sia Karamalegos
• Andrea Verlicchi
• Ivailo Hristov
• Karlijn Lowik
• Eric Goldstein
• Simeon Totev
• Michal Mocny
• Dan Freeman
• Philip Tellis
• Georgi Petrov
• Paul Calvano
• Edwin Molina H.
• Matt Zeunert

Agenda

• RUM CG meetup at perf.now() (RUM RUM)
• Barry's Bytes
• RUM Archive

Admin

• Skipping November 2025
• Next meeting: December 2025

AI Notes

Rum Rum Meetup and Community Engagement

The upcoming RUM RUM Real User Meetup in Amsterdam is set to foster stronger in-person connections and broaden community involvement ahead of the December meeting (03:38).

• Sign-ups have reached around 60 attendees, close to the cap of 70, with about 15 to 20 newcomers not yet part of the group (07:00)

• Karlijn emphasized the informal nature of the event aimed at reviewing the past year’s progress and planning future discussions.
• Attendees are encouraged to cancel early if they cannot attend to free spots for others.
• The event’s success is seen as a way to boost participation and deepen engagement beyond virtual meetings.

• Barry Pollard highlighted complementary sessions by the DevTools team on MCP and site-wide performance measurements with about 12 to 15 spots left, offering a pre-meetup opportunity for deeper technical exchange (09:07)

• This smaller group session precedes the Rum Rum event and provides focused discussions.
• Karlijn noted around 10 people joined after recent outreach, signaling growing interest.

• The broader Perf Now conference expects about 220 to 260 attendees, with room to publicize further and attract more participants to the Amsterdam meetup (09:45)

• Barry clarified some attendees choose to remain private, explaining the discrepancy in visible sign-ups.

• The group plans to skip the November meeting due to TPAC and holiday conflicts, aiming to reconvene in December with potential follow-ups from Perf Now and TPAC learnings (03:56, 59:08)

• Nic Jansma will cancel November’s date and monitor interest for December topics.

• There is a strategic push to recap Rum CG’s yearly progress publicly and at TPAC, with Barry intending to share updates to raise awareness and encourage wider participation within the Web Performance Working Group (11:03)

• This aims to position the Rum CG more centrally in web performance conversations and attract more contributions.

Google and Browser Ecosystem Updates

Barry Pollard provided a broad update on key Google and browser platform changes affecting RUM tools and web performance measurement (12:43).

• Lighthouse v13 was released, marking a breaking change by dropping older audits in favor of combined Insights aligned with the Chrome Performance Panel (13:54)

• Users should update documentation links and test integrations to accommodate this shift.

• A new No-Vary-Search HTTP header proposal allows browsers (currently Chrome only) to treat certain URL parameters like UTM as cache-agnostic, potentially boosting cache hit rates and reducing origin server load (15:05)

• Barry recommends monitoring adoption and encouraging clients to leverage this to improve caching efficiency.

• The older “purpose” HTTP header has been retired in favor of “set-purpose”, which Chrome exclusively supports; RUM tools should adapt accordingly to avoid missing data (16:15)
• Speculation rules on mobile now use a viewport-based heuristic for prefetching and prerendering, increasing prefetch stats that RUM tools may observe (16:15)

• No action needed if speculation rules are already supported, but performance analysts should be aware of this shift.

• The CrUX dashboard is being deprecated, with the last update in October; users should migrate to alternative tools or BigQuery connectors while noting potential costs (17:31)

• Barry advises caution about cost and performance issues with BigQuery.

• An ongoing experiment on soft navigations is underway, and Barry urged RUM providers to actively test and provide feedback to influence final shipping decisions (18:46)

• Karlijn confirmed plans to ship around Perf Now, with Erin focusing on integration despite other backlog priorities (21:07)

• Plans for a simple selector string in event timing for improved IMP reporting will soon ship, providing fallback identifiers like tag names, IDs, or image src URLs to better capture user interaction targets even if DOM elements disappear (23:41)

• Philip Tellis confirmed this new field will require RUM tools to update parsing logic to benefit from it (24:21)

• Google is introducing a CPU performance API with broad device categories (high-end, low-end, etc.) to help segment performance data by device class without fingerprinting risks (26:51)

• This will enhance understanding of performance variations across device types.

• Barry noted the need for cross-browser coordination on Core Web Vitals and event timing specs, highlighting that Safari Tech Preview supports INP behind a flag but with performance quirks being addressed (29:53)

• Clarifications on LCP edge cases are ongoing, with browser vendors refining spec implementations to improve consistency (30:35)

• Firefox and Safari adoption of Core Web Vitals and event timing APIs are advancing, promising richer cross-browser RUM insights soon (30:35)
• Barry shared tips for debugging React sites using new DevTools Performance Panel features, aiding performance troubleshooting beyond RUM data (35:50)

RUM Archive Project Progress and Strategic Vision

Robin Marx and Nic Jansma detailed the RUM Archive’s evolution, emphasizing its role as an open, anonymized dataset aggregating real user metrics from Akamai’s mPulse product and other contributors (36:50).

• The archive now includes daily uploads of three datasets: aggregated page loads, third-party resource timing, and recently added individual site-level raw RUM data from personal projects (41:41)

• The individual site data helps counteract biases from aggregated data focused on Akamai’s top 100 customers, which skew heavily towards mobile and iOS.

• Data stretches back to 2021 with near-daily updates, enabling longitudinal analysis of real user performance across multiple sites and browsers (41:38)
• The archive fills a gap in the ecosystem by providing real user data complementary to synthetic datasets like HTTP Archive and CrUX, supporting multi-browser, multi-device views (43:40)
• Access is via Google BigQuery with helper functions and comprehensive documentation, though some users face a learning curve querying the data’s structure (43:40)
• Robin showcased insights such as:

• Browser update adoption rates, with Chrome users reaching 75-90% adoption quickly versus slower Safari uptake and Firefox long-term support versions affecting update cadence (44:50)
• Geographic breakdowns of Google Baseline feature support, revealing unexpected patterns like South Korea lagging despite advanced infrastructure (49:00)
• Correlations between browser versions, baseline features, and actual feature usage on pages, though some Chrome usage stats may be inflated due to measurement methodology (48:50)

• The project is actively seeking more data contributors beyond Akamai, highlighting Cloudflare’s recent announcement to share RUM data freely and inviting personal site owners to participate (53:50)

• They stress privacy safeguards and manageable integration effort to encourage broader participation.

• Robin and team plan to enhance the archive with additional default graphs, baseline feature analyses, speculation rules data, screen size dimensions, and usability metrics over the coming year (55:30)
• Usage is currently lower than expected, and the team welcomes feedback on barriers and ideas to increase adoption, including presentations at Perf Now and TPAC (51:30)

• Cliff speculated that wider Core Web Vitals data from Safari and others could boost interest, as CrUX remains the dominant public data source for now (52:20)

• The archive aims to be a neutral, community-driven resource rather than proprietary data, fostering cross-company collaboration for better RUM insights (53:50)
• The team will demo the archive at Perf Now’s Google booth for further outreach and feedback (58:50)

Meeting Logistics and Future Planning

The group agreed to skip November due to TPAC and holiday conflicts and tentatively schedule the next meeting for December, with the agenda to be shaped by conference outcomes and community input (03:56, 59:08).

• Nic Jansma will send a cancellation for the November meeting and gauge interest for December topics (03:56)
• Attendees were encouraged to propose topics or lead discussions via the group’s topic backlog and voting system to guide future agendas (06:04)
• The team expressed enthusiasm for the upcoming in-person events to strengthen collaboration and knowledge sharing despite some members unable to attend (58:53)
• Karlijn shared that Fridays are now her day off but plans to attend some meetings occasionally, reflecting ongoing commitment (01:00)

Action items

Barry Pollard

• Share Google DevTools MCP sessions link with interested attendees (09:30)
• Continue seeking feedback and validation on the soft navigations experimental API; encourage RUM providers to test and provide input (18:40)
• Update Web Vitals JS to read new selector identifier field once available (24:45)
• Follow up with Google team on fixes and accurate data for Chrome usage API feature statistics (popover API issue) (56:35)

Karlijn Lowik

• Monitor and communicate questions regarding Web Vitals 5 and soft navigations origin trial during event season, especially around Perf Now (21:20)
• Send signup and event details for Rum Rum meetup attendees (09:25)

Nic Jansma

• Cancel November RUM CG meeting and schedule December meeting with potential agenda on TPAC and Perf Now follow-up (03:56)
• Publicize Rum Rum meetup and encourage signups to reach capacity (10:00)
• Set up and share public version of the Rum Archive presentation to facilitate external participation (00:37)

Robin Marx

• Continue publishing daily updated anonymized RUM Archive datasets and visualizations for community use (40:30)
• Provide demo sessions of RUM Archive project at Perf Now and Google booth to increase awareness and engagement (58:40)
• Encourage community feedback and contributions to expand the RUM Archive dataset and capabilities (53:30)

Cliff Crocker

• Support dissemination and discussion around Rum Rum meetup and TPAC session plans (06:31)

Michal Mocny

• Assist with clarifications on soft navigations origin trial tokens and confirm stability or expiry (20:00)
• Provide technical input and feedback on LCP and paint timing edge cases across browser implementations (30:55)

All Participants

• Engage with RUM Archive data for insights and consider potential data contributions (54:00)
• Review updates from Chrome, Safari, and Firefox event timing features and planning for future Web Vitals metrics integration (29:00)