Sentinel: Your Web-Performance Watchman


I’ve done a lot of great work with a lot of great people, but don’t just take my word for it—here’s what they had to say about me:


We engaged Harry to help with site-speed and take a deep, specialist dive into our codebase. Having spent many years in the industry, and being in receipt of numerous reports where we need to repeatedly ask for amendments and clarity over a number of versions, I was thrilled to receive the high-end report he produced—not one change was requested!

It is of such a high standard: easy to read, gives clear and direct advice for points of action, and explains the investigated areas in such a way that it is accessible for all, technical or not. Thank you, Harry—this is a career first for me not having to ask for the report to be redrafted so that it’s usable!

Anna O’Connell, Scrum Master, MKM

Southern Alberta Institute of Technology

Thank you so much for the excellent session, Harry—it was a lot of fun. The team was jazzed by what they learned and were amazed by how prepared you came and all of the ideas you helped spark for ways forward.

We appreciated your thoroughness, insights, expertise, and the thoughtfulness you brought towards your prepared materials.

— Jonathon Olenick, Manager, Digital Experience, Southern Alberta Institute of Technology


Harry helped our team level up their scalable CSS architecture skills, and to say that he had a large impact on our work is an understatement. We can’t recommend him enough.

Addy Osmani, Google


We engaged Harry to provide our go-to-market teams insight into the latest industry web performance challenges and tuning and debugging techniques to address them. Harry’s infectious passion and knowledge for the subject shone through, and he left us equally as excited and passionate to share our new found knowledge with customers. We look forward to working with Harry again in the future.

Michael Gooding, Akamai

Smashing Magazine

Harry is very knowledgeable, experienced, and hard-working, with a vivid passion for web performance, tooling, and productivity. We’ve received incredible feedback from his sessions and the insights he kindly shares. Highly recommended!

Vitaly Friedman, Smashing Magazine

BBC iPlayer

Harry gave the team a strong footing for identifying performance issues on iPlayer. With his knowledge, we were able to roll out quick fixes to our audiences without the need for big rewrites, all within just two days.

Matthew Burrows, BBC iPlayer

Beyond Tellerrand

I could start and say how great it is to work with Harry on projects, but I assume many other people before me did this already. Therefore I’d like to mention the many reasons why it is great to have Harry Roberts be a part of your events.

Harry is a reliable and well prepared speaker who finds the right balance between giving a technical talk and still entertaining the audience. He’s never let me down and always come in on time. Next to the things I mentioned and which are obvious, it is important for an event organiser like me to have speakers at your events that engage with the audience and do not hide backstage, for example. For the delegates, one of the best things at such events is when speakers are accessible, and when they can ask questions and exchange after a talk is done. This is what Harry also is excellent at and never disappoints.

But most importantly over the last nearly-ten years, Harry became a close friend of mine and I am always happy and looking forward to seeing him!

Marc Thiele, beyond tellerrand Events


Harry is a truly inspired and gifted teacher, and a web performance master. He is gracious and patient, taking the time to answer every single question, always making you feel comfortable and easy. The web performance workshop was so complete and comprehensive, it covered every aspect of performance-first development. What became clear very quickly, is Harry’s completely holistic approach to web performance, where every single development decision is questioned and tested, to ensure it is performance driven. The workshop has helped me change my career path by giving me the tools, the knowledge, the confidence and the skills necessary to work and grow in the web performance field.

Harry brings a lot of brevity and lightness to his workshops, they are fun, inclusive and very inspiring. At the beginning I called Harry a teacher, but during and after the workshop, it felt like he was not just a teacher, but a mentor. And that is priceless. I encourage anyone who is serious about web performance to take a workshop with Harry Roberts.

— Zach Miller, Front-end Developer, Superfein

Tim Kadlec

There is a short list of people I whole-heartedly recommend for detailed performance work and Harry is right there at the top.

Tim Kadlec, Web Performance Consultant


We approached Harry as although we had a good grasp of the fundamentals of web performance as a team, we needed to dig deeper. We got Harry in for a two day on-site and were hugely impressed by the depth and breadth Harry was able to cover in such a short time. Crucially, we were left with a long list of tangible actions to take away which have since resulted in a measurable improvement in the performance of our sites across the board.

Barry McGee, Senior Web Developer, Canonical


Harry’s workshop was excellent; we left with tons of new ideas and techniques to improve both the CSS architecture and overall performance of Behance and Adobe Portfolio.

Jackie Balzer, Adobe


When we first connected with Harry, he was a totally unknown quantity to us—he’d simply met one of our UX designers at a conference and mentioned that he might be able to help us with some site-speed issues we were facing. A few weeks later and he was sat in our office in Tallinn, digging into the problems right there alongside our engineers.

The impact of his work cannot be overstated. Within just a matter of days he’d identified and rolled out fixes that took global load times down from 18 seconds to just six. The results of his work could be seen immediately in our KPIs and showed a severalfold return on investment after no time at all.

But, he wasn’t ready to stop there: after focusing on tactical and high-return tasks, he turned his attention to longer-term strategic goals, including geographic monitoring and fostering a performance culture within the business. He always spoke about we, fully embedding himself in the team and making himself a core member. It really felt like he was there with us the whole time.

He works quickly, methodically, and incredibly forensically, and has a wonderful ability to manage both the business- and technical challenges of web performance. Though clearly technically very proficient, his ability to speak in relevant and jargon-free dialogue allowed him to pull all facets of Coingaming together to better understand and support site-speed efforts. From Business Insights to Marketing, Product to Engineering, and right up to me, the CEO, everyone was left aware of the importance and impact that site-speed has on our business.

He has remained a part of Coingaming in some way for over two years now: we’ve rehired and retained him a number of times to help keep us on the right path as our business scales and evolves, and as we add new products and team members to our family.

Tim Heath, CEO & Founder, Coingaming

Better Collective

We worked with Harry for one incredible week, in which we created a tailor-made CSS framework from scratch, complete with naming conventions, documentation style, attributions and an object oriented architecture. Pretty impressive, especially considering that we were only three persons: Harry, a designer and a product manager. Harry was the driving force behind the architecture and for every question we asked, he had well-thought out answer. We managed to make decisions very quickly, which enabled us to move extremely fast toward actual implementation. Without sacrificing quality in any way.

Working with Harry made us confident that what we are building will last and be a pleasure for us to work with, and for the next person joining the project. So far, we are still enforcing the rules and methods, we learned from Harry and we are loving it!

Alette Holmberg-Nielsen, Better Collective


I’ve worked with Harry on numerous projects over the years and each time he brings huge amounts of value with his detailed knowledge of performance and front-end architecture. Specifically, on the NHSx project, the techniques I learned surrounding ITCSS changed the way I build web applications. Without a doubt, Harry is the consultant you should bring in if you want an authority on how to build well-architected, fast web apps.

Josh Nesbitt, Consultant, Stac

Web Summer Camp

Harry held a full day workshop at Web Summer Camp, an event I organize every year. I knew about his expertise on optimizing performance of web sites beforehand, but he still blew me away with overwhelming details he delivered and the dedication to share his knowledge to the crowd. The workshop was to be six hours long but he continued for two more hours and most participants remained to hear his valuable advice, tips, and tricks. Some of them were literally applying his advice on their projects during the workshop and doubling the speed of their sites.

But what I like most about Harry is that he is a very approachable and friendly person, great to communicate with, all in all, a great bloke.

Ivo Lukač, Web Summer Camp

Jannik Lehmann

I visited Harry’s Web Performance Masterclass and can’t recommend it enough. It has been five sessions where we really focussed on the topic, what it’s about, and how to handle things best. Harry wouldn’t end the workshop before making sure literally every last question was answered, and there were very few questions he didn’t have an answer for. In the rare event that he didn’t, he really cared and made a great effort to provide an answer at the beginning of the next session.

The vibe on the workshop was really nice, I blame this on Harry quite a bit: his endless patience and impressive in-depth knowledge on the topic made it a really valuable experience. The resources we got were great, it was easy to follow along, it was well prepared, and made the deep-dive feel really easy.

Jannik Lehmann, Freelance JavaScript Developer and Consultant


Spending a week with Harry has turned my approach to large CSS projects on its head. For years I’ve struggled to find a way to effectively structure large, complex CSS projects and his ITCSS methodology has delivered. Now I have a small, flexible SASS codebase and more performant CSS. Whilst guiding me with ITCSS, Harry dropped in many nuggets of CSS & SASS wisdom which were excellent and will prove invaluable to me in the future. I now feel equipped to use Sass & CSS in my development workflow with the most challenging projects.

Justin Waugh, UNOPS

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!


  • inuitcss
  • ITCSS – coming soon…
  • CSS Guidelines

Next Appearance

  • Talk & Workshop

    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.