What is a design system and when does it pay off? Lessons from GOV.UK, REA and Allegro

What is a design system

Nielsen Norman Group, one of the best-known usability research firms, describes a design system as a complete set of standards for managing design at scale with reusable components and patterns (“Design Systems 101”). In most companies that boils down to three layers. Colours, typography and the logo form the visual base. On top of it sits a component library, with buttons, form fields and cards that someone designed and coded once so nobody has to redo them. Patterns then explain how those pieces fit into bigger parts of a product, like the navigation or an order form.

What you don’t see in the files are the people. Somebody has to look after the system, fix what breaks and add what’s missing; leave it alone for a year and it ends up describing a product you no longer have.

Design system, brand guidelines and UI kit

People mix these three up constantly, and it’s easy to see why. A brand book shows what the brand looks like, logo, colours, fonts and all. Designers keep their interface elements in a UI kit, which is really just a file. A design system goes further than either of them, because it ties the visuals to code and to rules of use, and somebody owns it. Figma’s own introduction to design systems places the style guide inside the system as the part that handles visuals, with coding and usability standards next to it.

Day to day, the print shop and the agency reach for the brand book. The design system is for the teams that ship new screens, pages and campaign materials every week.

How much companies with one save

Australia’s REA Group, which runs property portals, has measured this most thoroughly. Chris Stonestreet, who leads design systems there, showed at the Web Directions conference in 2023 how the company measures the value of its Construct Kit system. Around 58 designers and 319 developers working across four brands use it. By the company’s own calculation, the system has saved around 300,000 hours of design and development time since 2018. Work on a new home page shrank from around 240 to 60 developer days.

Headspace, the meditation app company, reports similar numbers in a case study published by Figma. An average design file there is 85 percent tokens and components from the design system. Simple tasks take 20 to 30 percent less time, and complex ones up to half the time. Preparing light and dark mode used to take an hour and now takes a minute. One engineer estimates that releases have sped up by 30 percent.

These figures come from the companies themselves, so read them with some caution. Two older experiments are more controlled. In a 2019 test by Figma’s team, designers with access to a design system finished a task 34 percent faster, although Figma itself notes that this is the upper limit, because the system fitted the tasks perfectly. The agency Sparkbox asked eight developers to code the same form twice, once from scratch and once with IBM’s Carbon system. Working with the system, they were 47 percent faster. Eight people and one form is a tiny sample, of course, yet none of these results points the other way.

A rebrand without reworking every page

You can see the effect clearly in the UK government. Its GOV.UK Design System gives public sector teams one set of components for their websites, and by 2020 more than 300 services were built on it. The Government Digital Service put the savings at around £17 million a year.

When GOV.UK began refreshing its brand across its products in June 2025, teams already on a current version of the system had nothing to do. The new look simply came with the update, and the instructions for them took one sentence.

“You do not need to take any action.”

For a company considering a rebrand, this may be the most important lesson. Without a design system, new colours and fonts have to be applied by hand on every page, in every app and in every template. With a system, most of the change happens in one place.

When a design system doesn’t pay off

Nielsen Norman Group says plainly that a design system makes sense when a company has years of repeatable design work ahead. For a prototype or a product with a handful of screens, a quick return is unlikely. A system also needs a dedicated team, because it doesn’t end on delivery day.

The biggest problem, though, is often that people don’t use it. In zeroheight’s 2026 report, based on a survey of 147 people working with design systems, adoption and awareness inside the company have topped the list of challenges for five years in a row. Three in five teams are understaffed, and only about 5 percent of them measure return on investment.

Spotify learned what happens when a system doesn’t fit the organisation. The central team behind its first system became a bottleneck for independent product teams. Once that team was disbanded, teams started building their own solutions, and at one point the company counted 22 of them. The way out was a family of systems with a shared foundation of colours, typography and tokens, which teams extend with their own parts. Allegro knows the maintenance cost too. Its team wrote on the company’s engineering blog that the shared styles of its Metrum system sped up page loads, but made updating dependencies much harder.

Why AI makes design systems matter more

Until recently, design systems were used by designers and developers. Today AI agents use them more and more, building screens and materials at the request of marketing, sales or a product manager. Without a system, every agent guesses colours, spacing and buttons. We described this with the BILL example in our post on design systems for AI agents.

Allegro is modernising its system with exactly this in mind. Marcin Łasica, who leads design excellence there, says in a conversation summarised by Netguru that the company treats AI as a full user of the design system from the very start. Names, structure and constraints are meant to be written so that models assemble on-brand interfaces. Uber used AI from the other side and had it document its Base system. An agent connected to Figma produces component specifications in minutes instead of weeks.

A study presented at the CHI conference in 2026 adds an interesting result. Researchers in Seoul compared three ways of giving a language model a design system. A registry of ready-made components came out best, with 95 percent compliance, ahead of a plain description of the rules. Large companies are already acting on this: Atlassian and GitHub publish MCP servers through which agents fetch the components and tokens of their systems (Atlassian Design System, Primer).

How to tell whether your company needs one

It helps to start by counting. How many screens, pages and templates does the company produce in a year, and how many teams are involved? A single website that changes twice a year doesn’t need a design system, since a solid visual identity and a handful of templates will do. It’s a different story when the product grows with every sprint, marketing wants new landing pages each week and three departments are already using AI. In that situation a system tends to pay for itself quickly.

Building everything at once isn’t necessary either. Tokens (colours, typography and spacing stored as named values) and the components you use most are a reasonable start, together with one person who owns the system and a simple number to track, for example how many new screens are assembled from existing parts. We design such systems together with the interface as part of our UX/UI design work, and in our AI design workflows service we make sure AI tools use them too. That is the consistency without policing area.