GTmetrix alternatives: 11 tools to compare

Who this list is for: developers and agencies watching client sites

When a client emails to say their homepage feels slow, you need more than a single test result. You need history, so you can show what changed and when, and you need alerts, so you hear about a slowdown before they do. GTmetrix is a familiar name in speed testing, and it's worth comparing what else is out there once you're responsible for lots of sites.

I've written this for web developers, freelancers and small agencies who monitor speed for other people's websites. The question isn't which tool produces the prettiest waterfall chart. It's which one helps you catch problems early, explain them to a client and prove the fix worked.

Sorting the eleven by the monitoring job

• Speed history and Core Web Vitals: Calibre, DebugBear, SpeedCurve and Treo are pitched at tracking site performance, while Sitespeed.io is an open source option.
• Synthetic checks from many places: Catchpoint, Dotcom-Monitor and Uptrends monitor from multiple locations, so check what each covers before you trial it.
• Uptime and wider infrastructure: Sematext, Site24x7 and UptimeRobot watch whether sites are up and, in some cases, the servers behind them.

Many agencies end up pairing one tool from the first group with one from the third. A speed tracker tells you a page got heavier after a plugin update, and an uptime monitor tells you at 2am that the site went down. Those are different alarms, and few tools do both equally well.

GTmetrix replacements for agency monitoring, A to Z

These are listed in no particular order beyond alphabetical, each with one line on who it's built for.

Calibre

Best for: Agencies that want real user monitoring, Google CrUX data and synthetic page speed tests together.

Catchpoint

Best for: Organisations that want to monitor performance, availability, reliability and reachability from where their customers are.

DebugBear

Best for: Developers tracking Google Core Web Vitals with synthetic tests and real user monitoring.

Dotcom-Monitor

Best for: Site owners who want real-browser checks from multiple locations and instant alerts about downtime.

Sematext

Best for: DevOps teams who want live visibility into their IT infrastructure.

Site24x7

Best for: Agencies who want to monitor websites, servers, networks, applications and cloud platforms in one account.

Sitespeed.io

Best for: Developers who want an open source tool to analyse and optimise site speed against performance best practices.

SpeedCurve

Best for: Performance leads who want to see how people experience the speed of their website, on mobile and web.

Treo

Best for: People who want to track their site, as the vendor puts it, and should check what it covers before a trial.

UptimeRobot

Best for: People who mainly need SSL, keyword and cron monitoring with alerts by email, SMS or Slack.

Uptrends

Best for: Monitoring leads watching web and API user journeys from ISP-based locations worldwide.

Quick comparison by test approach

Tool	Test approach	Good for
Calibre	Real user and synthetic	CrUX data plus page speed tests
Catchpoint	Performance monitoring	Availability and reachability
DebugBear	Core Web Vitals tracking	Synthetic tests and real user monitoring
Dotcom-Monitor	Real-browser checks	Downtime alerts
Sematext	IT system monitoring	Infrastructure visibility
Site24x7	IT environment monitoring	Sites, servers and networks
Sitespeed.io	Open source tool	Speed analysis and optimisation
SpeedCurve	User focused observability	Seeing how visitors experience speed
Treo	Site tracking	Check what it covers in a trial
UptimeRobot	Uptime monitoring	SSL, keyword and cron alerts
Uptrends	Synthetic journeys	Web and API user journeys

Lab tests, field data and why clients get confused

A lab test runs a page in a controlled browser from a chosen location. Field data, such as Google's Chrome UX Report, reflects what real visitors experienced. The two often disagree, and that's where client conversations go wrong. A client sees a lab score that looks poor, panics, and asks you to fix something their real visitors never noticed.

If you report on speed to clients, choose a tool that can show both, labelled clearly. Lead with what real visitors experienced, then use lab tests to explain the cause. It's a calmer conversation and it keeps your work focused on changes that help the people using the site.

Caching headers belong in every speed report

A lot of slow pages are slow because the browser has to download the same files again on every visit. The IETF's RFC 9111 on HTTP caching defines how caches work and the header fields, such as Cache-Control, that tell browsers and CDNs what to keep. When you trial a tool, check that it shows response headers for each file clearly, so you can spot a missing or misconfigured cache rule in seconds rather than digging through raw data.

What to check during a trial

• Can you group sites by client and share a read-only view with each one?
• Does it test from the regions where your clients' customers live?
• Can you schedule tests on mobile and desktop profiles separately?
• Do alerts go where your team already works, such as Slack or email?
• Can you mark a deploy or plugin update on the timeline, so a slowdown has an obvious cause?

For one-off checks rather than ongoing monitoring, my list of website speed test tools covers quick testers, and if you document visual changes for clients too, these website screenshot tools are worth a look.

My advice for agencies moving on from GTmetrix

Pick one tool for speed history and one for uptime, rather than hunting for a single product that claims to do everything. Set them up on your three most important client sites first, live with the alerts for a couple of weeks, and only roll out to the rest when your team trusts what it's seeing. Noisy alerts get ignored, and ignored alerts are worse than none.

Do you make website speed or performance monitoring tools? Tool makers can ask to be considered for a featured place on this list.

Want your tool on this list? Featured spots and reviews here are paid partnerships. Here's how to partner with me.

Frequently asked questions

Why do lab speed tests and real user data disagree?

Lab tests run in one controlled setup, while real user data reflects many devices, networks and locations. Both are useful. Real user data tells you what visitors experienced, and lab tests help you find the cause.

Do I need uptime monitoring as well as speed monitoring?

For client work, usually yes. Speed tools tell you a page got slower over time, while uptime tools alert you when a site stops responding. They answer different questions.

How often should I test client sites?

Daily scheduled tests are enough for most small business sites, with extra tests after a deploy, theme change or plugin update. Uptime checks should run every few minutes.

What should a speed report for a client include?

Real visitor experience first, then the main causes found in lab tests, the fixes you made and a before and after comparison. Keep the jargon short and explain what the change means for their visitors.