Core Web Vitals Practical Monitoring 2025 — SRE Checklist for Enterprise Projects

By 2025, Core Web Vitals have become a contractual requirement rather than a nice-to-have metric for web production partners. Largest Contentful Paint (LCP), Interaction to Next Paint (INP), and Cumulative Layout Shift (CLS) must be expressed as SLOs that tie directly into day-to-day delivery workflows. This guide distills an SRE perspective for multi-region production teams that ship, optimize, and operate image-heavy experiences.

TL;DR

• Define SLOs across LCP/INP/CLS plus error rate, and assign ownership that spans web, CDN, and image pipelines.
• Build a three-layer metric stack—Real User Monitoring (RUM), synthetic checks, and logs/traces—and correlate it with image swaps and cache invalidations in seconds.
• Unify runbooks between image delivery teams and SREs so threshold breaches trigger deterministic decisions and escalation paths.
• Publish business-aware weekly reports to maintain transparency with stakeholders and unlock additional optimization budget.

1. SLO design — expectations and error budgets

Metric	Target (Mobile)	Source	Notes
LCP	p75 ≤ 2.3s	RUM + CrUX	Instantly reflects server rendering and image optimization changes
INP	p75 ≤ 200ms	RUM	Keeps pace with lazy loading competitiveness and post-load interaction
CLS	p75 ≤ 0.1	Synthetic	Detects layout shifts caused by placeholders and ad swaps
Error rate	< 0.2%	CDN logs + APM	Includes image workers and edge runtime exceptions

• Track a monthly error budget, pausing new feature rollouts once consumption exceeds 60%.
• Map core KPIs such as conversion rate or lead volume to affected templates to make business impact explicit.

2. Building the observability stack

Real User Monitoring (RUM)

• Embed the Web Vitals library in Next.js and stream measurements per locale into a Measurement Protocol endpoint.
• Use Looker Studio dashboards to inspect device/region distributions and isolate LCP bottlenecks.

Synthetic monitoring

• Schedule Playwright + Lighthouse CI runs every 15 minutes on critical journeys.
• Pair each journey with the [performance-guardian](/en/tools/performance-guardian) CLI so asset regressions and latency spikes are flagged instantly.

Logs and traces

• Instrument Next.js Edge runtime with OpenTelemetry, exporting fetch durations and cache hit ratios for LCP resources into BigQuery.
• Store metadata-audit-dashboard results in the same warehouse so metadata gaps can be correlated with LCP regressions.

3. Operations workflow and runbook

Incident detection

1. RUM shows LCP p75 breaching the 2.3s threshold.
2. PagerDuty alerts the on-call SRE and mirrors the event into the Core Slack channel.
3. Linked dashboards highlight impacted locales and templates on the spot.

Escalation example

Stage	Action	Timebox
Triage	Use image-trust-score-simulator to confirm asset integrity and rule out cache corruption	15 min
Mitigation	Image delivery team swaps to high-performance variants or purges the affected CDN path	30 min
Recovery	Synthetic checks validate improvements, and RUM confirms p75 sliding back under target	60 min
Postmortem	Document RCA and preventive actions in Notion within 24 hours	24 hours

Runbook snapshot

• LCP regression (image): next/image response weight jumps, fallback S3 region latency, or missing metadata forces AVIF→JPEG.
• INP spike (JS): Hero lazy load collides with interaction handlers—fix with priority hints and controller isolation.
• CLS breach: Ad container lacks reserved height—update placeholder CSS and leverage aspect-ratio.

4. Reporting and governance

• Weekly review meetings surface SLO attainment, error budget consumption, and revenue impact via dashboards.
• Highlight regional wins for clients—for example, how APAC LCP improvements lifted CVR by 4%—to justify continued optimization investments.
• Archive weekly reports automatically into GCS buckets and align them with internal OKRs.

5. Next implementation steps

1. Auto-generate SLO templates for every new engagement by seeding GitHub issues at project kickoff.
2. Blend WAF/edge logs to automatically tag bot-driven LCP regressions.
3. Version image assets—feed [performance-guardian](/en/tools/performance-guardian) regression findings directly into pull request comments.

Summary

Operationalizing Core Web Vitals inside an SRE discipline enables production teams to:

• Honor contractual SLAs,
• Speed up collaboration between design, engineering, and delivery partners, and
• Provide sharper, data-backed recommendations to clients.

Use this playbook as a baseline, tailor runbooks and metrics to each engagement, and stay ahead in the 2025 performance race.