Design Systems at Scale – With Stefano Magni (Preply)

🎧 New Señors @ Scale Episode

This week, I spoke with Stefano Magni, Senior Front-End Engineer & Tech Lead at Preply, about what it really takes to build and scale a design system that serves millions of learners worldwide.

We covered everything from rebrands and metrics to culture and collaboration — and why working in public can transform your career.

⚙️ Main Takeaways

1. Your career = skills + reputation + network.
Stefano’s core belief: if you ignore any of these three, you limit your growth. Working in public builds the reputation and network part most engineers neglect.

2. Design System Visual Coverage.
Preply measures the real impact of its design system by tracking what percentage of the UI comes from system components — a data-driven approach to adoption.

3. Building fast meant technical debt — intentionally.
During Preply’s massive rebrand, the team shipped quickly with Radix UI and accepted debt consciously to meet deadlines, planning future cleanups in advance.

4. Pragmatism over perfection.
Pixel-perfect is nice, but at scale, pragmatism wins. The key is knowing what matters and what can wait without compromising experience.

5. Managing large codebases without tests.
At WorkWave, Stefano learned how to maintain 250k+ LOC apps safely using strict TypeScript patterns and consistency — not tests — as the safety net.

6. Metrics drive everything at Preply.
Every initiative — from UI improvements to accessibility — ties back to measurable outcomes. “You don’t just build something; you build it to move a metric.”

7. Accessibility through measurement.
Accessibility violations are tracked directly from users’ devices, creating accountability and visibility company-wide.

8. Engineering Excellence is now cultural.
Preply evolved from a “hackers” culture to one of Keep Perfecting — prioritizing quality, accessibility, and speed without sacrificing long-term scalability.

9. Duplication beats bad abstraction.
Stefano argues that a few well-understood duplications are better than the wrong abstraction. Clean code isn’t always DRY — it’s maintainable.

10. Public work accelerates careers.
From Stack Overflow to conference talks, Stefano shows how sharing your process publicly compounds into reputation, opportunities, and impact.

🧠 What I Learned

• Metrics give direction — not judgment.
• Accessibility and performance should be tracked like business KPIs.
• Teaching is the best way to master your craft.
• Duplication done right can be an act of clarity.
• Public work is career leverage disguised as learning.

💬 Favorite Quotes

“Your career depends on three things — your skills, your reputation, your network.”
“Design is an approach, not a role.”
“We intentionally created technical debt — because we had to deliver.”
“Duplication isn’t the enemy. Wrong abstractions are.”
“It’s not about what you know or who you know. It’s about who knows you and what they know you can do.”

🎯 Also in this Episode

• How Preply rebranded 70% of its product in one cycle
• Why frontend engineers need to think socially
• The hidden value of data-driven experimentation
• Building for accessibility at scale
• Engineering culture shifts — from hacking to perfecting

🎧 Listen Now

🎧 Spotify
📺 YouTube
🍏 Apple Podcasts

Episode Length: 1h 4m on design systems, engineering culture, and public work at scale.
If you care about design systems, accessibility, or how engineering culture evolves with scale — you’ll enjoy this one.

Happy scaling,
Dan