Sentinel: Your Web-Performance Watchman

Sentinel: Your Web-Performance Watchman

I focus on site-speed so you don’t have to.

Keep getting hit with performance regressions? Site-speed unstable and inconsistent? No time to triage performance issues? No one taking ownership of site-speed? Sound familiar?

Even the most performance-conscious teams rarely have the time or resources to:

  • define appropriate performance budgets;
  • procure and set up monitoring software;
  • identify regressions;
  • separate signal from noise;
  • triage performance issues.

That’s why they use Sentinel.

Outsource your performance monitoring to me, your web-performance watchman.

What is Sentinel?

sentinel /ˈsɛntɪnəl/
A soldier or guard whose job is to stand and keep watch.

Most companies simply don’t have dedicated performance teams (or even individuals) to keep a constant eye on site-speed. Engineers have product and feature work to do, and even with the best will in the world, performance ends up falling off the radar. Regressions sneak in, go unnoticed, and never get fixed.

Service undersells what Harry is providing here. It looks like a comprehensive monitor/triage/root-cause/impact high-touch service from one of the best.

Patrick Meenan

Sentinel is a service I offer to a small number of trusted clients: I become your eyes and ears so you can get on with what you do best. Using my own monitoring, I’ll work with you to define performance budgets and set up relevant dashboards and alerts to make sure you stay fast.

The moment a regression is detected, I receive the alert and get to work. Your developers don’t get interrupted by emails from monitoring software, and they don’t need to wade though meaningless data to uncover meaningful insights. In fact, they don’t need to do anything at all—that’s my job.

I’ll jump in, honing right in on the issue using bespoke dashboards and performance budgets designed specifically for you. I’ll identify the problem and hand over a report containing the timing of the regression, its cause, its severity, its impact, and its fix.

Learn more…

What Does Sentinel Look Like?

There are three key aspects to Sentinel.


Firstly, I’ll conduct an initial audit of your site to identify and address any current slowdowns—there’s no point monitoring a slow website!

Then, we work together to outline the key metrics we’d like to track. Want to monitor Largest Contentful Paint? Sure! TTFB? You got it! Total Blocking Time? Done! Once we have a handful of metrics we’d like to keep an eye on, we gather key pages to monitor—we could monitor all metrics on all pages, or any permutation of the above. It’s entirely up to you.

Once we have our key metrics, it’s time to set some budgets. Most teams find performance budgets paralysing, but that’s not your job anymore—it’s mine! I’ll calculate relevant budgets for each of our chosen metrics, and set up the corresponding dashboards and alerts for them.


Now, we wait.

If any of our key metrics regress beyond our budgets, I get alerted immediately. Alerts get sent to an expedited email address (that you also have access to), shooting right to the top of my inbox.

From there, I begin analysing data, comparing charts, and running tests. I’ll cross-reference many different vectors to hone in on the problem, working out what happened and what might have caused it.

Once I have a reasonable idea of the issue and its solution, I’ll put together a report and send it over. This could be via email, or directly into your issue tracker. It’s entirely up to you.


What if we don’t have any regressions?!

This is great news! But don’t worry—you’ll never pay Sentinel for nothing. Regardless of how many incidents you experience, including zero, you’ll receive the following reports every month and each quarter:

Monthly, you’ll receive a general performance report. How many incidents did we have? How is the site faring compared to the previous period? Did the site behave consistently throughout the month? Did we notice any patterns? Do we have any opportunities outside of our key metrics?

Quarterly, you’ll receive a more comprehensive benchmarking report where we compare your site against competitors and industry peers. How do we stack up? Is anyone making great progress? Do we need to catch up to anyone? Can we identify any opportunities?

Arrange a call


Sentinel costs $5,999/mo.

  • USD
  • Billed quarterly
  • 20% discount for annual billing
  • Minimum commitment of six months

What’s Included?

  • Initial performance audit: We’ll conduct a thorough audit before we begin monitoring. This allows us to start from a healthy baseline.
  • Metric and budget definition: We’ll work out your key metrics and their corresponding budgets.
  • Monitoring software: No need to procure your own monitoring software—I have it covered already! I’ll set you up in my SpeedCurve and Treo accounts.
  • Always-on monitoring: The main event—I keep an eye on your performance budgets and tackle regressions as they happen.
  • Monthly status updates: At the end of each month, I’ll summarise the previous period. Is site-speed trending up or down? Did we improve on last month? Did we have more incidents than normal?
  • Quarterly healthchecks and benchmarks: Every three months, I’ll run a suite of tests against your closest competitors and peers to establish our position within your industry. Are we leading the pack? Or do we have opportunities for improvement?

Learn More

If you want to know more about Sentinel and how it can help your team, let’s arrange a zero-obligation call to discuss it further:

Let’s talk Sentinel

Hi there, I’m Harry Roberts. I am an award-winning Consultant Web Performance Engineer, designer, developer, writer, and speaker from the UK. I write, Tweet, speak, and share code about measuring and improving site-speed. You should hire me.

You can now find me on Mastodon.

Suffering? Fix It Fast!


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Next Appearance

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    WebExpo: Prague (Czech Republic), May 2024


I am available for hire to consult, advise, and develop with passionate product teams across the globe.

I specialise in large, product-based projects where performance, scalability, and maintainability are paramount.