---
title: "Core Web Vitals for Astro"
canonical: "https://lemwatch.com/monitor/astro/core-web-vitals"
framework: "Astro"
concern: "Core Web Vitals"
last_verified: "2026-08-11"
source: "https://lemwatch.com"
---

# Core Web Vitals for Astro

Field-data LCP, CLS, and INP tracking with regression alerts.

## Why this concern is different on Astro

Astro's default output is nearly perfect on Core Web Vitals — the regression usually comes from a client:load island that grew unnoticed. Since Astro ships zero JS by default, a single heavy island doubles your INP p75.

## Signals to watch

- INP regression traced to a client:load or client:visible island
- LCP shift when an integration like @astrojs/image is misconfigured
- CLS from View Transitions running before web-font swap

## What we check (universal)

- Largest Contentful Paint (LCP) — 75th percentile, tracked hourly
- Cumulative Layout Shift (CLS) — with the specific shifting element flagged
- Interaction to Next Paint (INP) — replaces FID for 2026 rankings
- Alerts fire when the 7-day rolling baseline degrades by >20%

## How Lemwatch helps on Astro

We track the specific route where CWV degraded, so you know which island to convert back to client:idle or server-only.

_Canonical HTML page: https://lemwatch.com/monitor/astro/core-web-vitals_