[ashtonanderson]

Turns PostHog web vitals back on, so we can see real-user CLS, LCP, INP and FCP per page. It's one line in src/lib/posthog-browser-config.ts:

capture_performance: { web_vitals: true, network_timing: false },

Why

capture_performance: false went in with the autocapture cleanup on 03-26 (815de5e). In posthog-js 1.257.2 a boolean there overrides the project setting, so vitals stopped even though they're still on in PostHog. Weekly $web_vitals events went from 20,900 (week of 03-09) to 9 (week of 04-20), and there have been 4 in the last 45 days.

Autocapture and pageleave stay off. Network timing stays off too, as it is today.

Cost

• Events: about 75,000 more a month, based on the 0.82 vitals events per pageview before March and about 91,000 pageviews in the last 30 days. The project sends about 260,000 a month now, and the free tier is 1 million.
• Page weight: PostHog loads web-vitals.js (about 4 KB compressed) after it starts. It isn't in our bundle.

What the data will look like

• Separate events: one page's metrics often arrive in separate $web_vitals events, so count each metric on its own.
• Fewer CLS samples: the SDK waits 5 s before sending, so a metric that reports as the visitor leaves can be lost. From 03-02 to 03-22 there were 19,861 events with FCP, 16,355 with LCP, 15,227 with INP and 9,057 with CLS.
• A rough "before": p75 across those weeks was CLS 0.78 and LCP 1.47 s, pooled across all pages and devices.

With #328

Draft #328 delays PostHog until the page is idle. It keeps using browserPostHogConfig and doesn't touch this file, so the two shouldn't conflict. Visitors who leave before PostHog loads wouldn't report vitals. The two haven't been tested together.

Testing

• npx tsc --noEmit, ESLint on the changed file and npx jest (76 tests) all pass, and CI is green.
• On the preview, in headless Chrome: web-vitals.js loads, the recorder script doesn't, and FCP, LCP, CLS and INP all arrived in PostHog for / and /puzzles. To get CLS I simulated hiding the page.
• These test events are in the production PostHog project under the preview's host. Their timings aren't meaningful.
• Not tested on production or on real phones.

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated
maia-platform-frontend	Ready	Preview	Nov 2, 2026 8:56am UTC