Stop finding out your website is slow from customers
Real user monitoring, Google’s Core Web Vitals data and synthetic tests in one place. Know when pages slow down, and see exactly what to fix.
Just need a one-off check? Get a free Core Web Vitals report.
Trusted by teams at
Know how fast your site really is
Real User Monitoring for your visitors, CrUX for Google’s view of any site, and Synthetic tests for fast feedback on every change.
Real User Monitoring
Core Web Vitals from every visit to your site. A small, privacy-first script, ready in minutes.
Learn about Real User Monitoring →Chrome UX Report (CrUX)
Google’s search data for any site, including competitors. Nothing to install.
Learn about CrUX Monitoring →Synthetic Monitoring
Consistent lab tests give you a steady baseline and fast feedback on every change.
Learn about Synthetic Monitoring →Know first, fix fast
Calibre points to the issues that matter most, so your team spends less time digging.
See what each release changed
Deploy markers on every Synthetic chart, and RUM split by release, show which deploy changed performance.
Learn about deploy tracking →Hear about changes first
Insights emails flag big changes across your sites every week, and Synthetic budgets alert you in Slack, email or webhooks.
Learn about Insights and alerts →Find the slowest interactions
RUM shows which buttons, links and inputs keep visitors waiting, and by how much.
Learn about element attribution →See what third parties cost you
Measure the size and main thread time of every tag, widget and script you didn’t write.
Learn about third-party tracking →Ask your performance data anything
Connect your coding agent to Calibre. Ask about any page and it finds the slow element, script or URL in your Synthetic, RUM and CrUX data, then writes the fix.
- Claude Code
- Cursor
- Codex
- Copilot
“Calibre delivers the substance behind the statistics. They know the actionability of performance measurement is paramount.”
“Thanks to detailed page breakdowns and filtering, I’ve found performance issues way deeper into customer journeys than I’ve seen before.”
“Now we can provide our clients with solutions, instead of setting up our own tooling.”
Built for the way your team works
SEOs
Track the Core Web Vitals data Google uses in search, and see which pages pass or fail.
Calibre for SEOs →Agencies
Monitor client sites, benchmark competitors, and show clients your progress.
Calibre for Agencies →Ecommerce
Find what slows product pages, search and checkout for real shoppers.
Calibre for Ecommerce →Product Teams
Make speed part of how you build, and see how each release changes it for real users.
Calibre for Product Teams →Developers
Performance checks in pull requests and CI, plus a CLI and Node.js API for everything else.
Calibre for Developers →Free tools for a quick check
Not ready for a trial? Check any site now, no sign-up needed. See all free tools.
Core Web Vitals Test
See whether a site passes Google’s Core Web Vitals, and how it does in each country.
Check a site →
Website Speed Test
Run a Lighthouse test from locations around the world, with audits that show what to fix.
Test a page →Fits into the tools you already use
GitHub
Get performance data in your pull requests.
Slack notifications
Send alerts to a Slack channel.
Zapier
Forward Calibre data and alerts to 5,000+ services.
Netlify
Mark deployments on charts and trigger tests.
Render
Test against deployment environments.
Webhooks
Send performance data to your own systems.
Node.js API
Build integrations and automate fetching data.
Command line interface
Manage monitoring from your terminal.
See your first results in minutes
RUM, CrUX and Synthetic on every plan, from US$75 a month. No credit card required.
