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Last updated on February 28, 2023
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Web Vitals API Reference

Learn how to use Web Vitals in Vercel Analytics with any frontend framework or project through the Web Vitals API.

Web Vitals in Vercel Analytics support Next.js, Nuxt.js, and Gatsby with zero configuration through build plugins. You can use Web Vitals in Vercel Analytics with any frontend framework or project through the Web Vitals API as shown below.

Measure web vitals

POST /v1/vitals

Send web vitals data to the Vercel Analytics Web Vitals API.

Getting Started

To use the Web Vitals API, you'll need to retrieve the analytics ID for your Vercel project. This value is exposed during the build and can be accessed by process.env.VERCEL_ANALYTICS_ID inside Node.js.

Inside your framework or Node.js script, you can then use this value in the body of your request to the Vercel Analytics Web Vitals API.

Note: vc pull does not pull VERCEL_ANALYTICS_ID as the Vercel Analytics ID environment variable is inlined during the build process. It is not part of your project Environment Variables, which can be pulled locally using Vercel CLI.

Example

You can view an example of the following code implemented inside our Create React App and SvelteKit starters.

vitals.js
import { getCLS, getFCP, getFID, getLCP, getTTFB } from 'web-vitals';
 
const vitalsUrl = 'https://vitals.vercel-analytics.com/v1/vitals';
 
function getConnectionSpeed() {
  return 'connection' in navigator &&
    navigator['connection'] &&
    'effectiveType' in navigator['connection']
    ? navigator['connection']['effectiveType']
    : '';
}
 
function sendToAnalytics(metric, options) {
  const page = Object.entries(options.params).reduce(
    (acc, [key, value]) => acc.replace(value, `[${key}]`),
    options.path,
  );
 
  const body = {
    dsn: options.analyticsId, // qPgJqYH9LQX5o31Ormk8iWhCxZO
    id: metric.id, // v2-1653884975443-1839479248192
    page, // /blog/[slug]
    href: location.href, // https://{my-example-app-name-here}/blog/my-test
    event_name: metric.name, // TTFB
    value: metric.value.toString(), // 60.20000000298023
    speed: getConnectionSpeed(), // 4g
  };
 
  if (options.debug) {
    console.log('[Analytics]', metric.name, JSON.stringify(body, null, 2));
  }
 
  const blob = new Blob([new URLSearchParams(body).toString()], {
    // This content type is necessary for `sendBeacon`
    type: 'application/x-www-form-urlencoded',
  });
  if (navigator.sendBeacon) {
    navigator.sendBeacon(vitalsUrl, blob);
  } else
    fetch(vitalsUrl, {
      body: blob,
      method: 'POST',
      credentials: 'omit',
      keepalive: true,
    });
}
 
export function webVitals(options) {
  try {
    getFID((metric) => sendToAnalytics(metric, options));
    getTTFB((metric) => sendToAnalytics(metric, options));
    getLCP((metric) => sendToAnalytics(metric, options));
    getCLS((metric) => sendToAnalytics(metric, options));
    getFCP((metric) => sendToAnalytics(metric, options));
  } catch (err) {
    console.error('[Analytics]', err);
  }
}