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Many businesses start with a tech stack that makes sense for their early-stage needs—fast to deploy, familiar to their team, and affordable. As a product scales and use cases evolve, however, the original stack can become a limiting factor.
That’s exactly what happened at Clarus R+D. The company had a growing user base, a clear market need, and a strong vision for the future. Their original app, built in Laravel (PHP) with a React SPA frontend, however, was no longer keeping up with the speed of business.
Ultimately, the solution was to rewrite their app using Elixir. That rewrite not only paid off in terms of app performance and team productivity but also gave the company a solid foundation that helped pave the way for an acquisition.
When the Stack Stalls Growth
Clarus launched with a clear business goal: to help companies find and optimize R&D tax credits. From startups to enterprise organizations, Clarus uses a custom digital product to efficiently identify potential tax savings for its users.
In the years after its initial launch, the Clarus team gained a deeper understanding of the problem their users needed to solve. As they continued to develop Clarus’ digital product to meet their users’ needs, however, technical debt gradually accumulated. The app became difficult to maintain and lacked the flexibility to support continued growth.
Performance issues started surfacing, especially in core areas of the product. One key feature, a calculation engine critical to delivering value to users, slowed down so dramatically that basic tasks began timing out.
A New Direction with Elixir
Ultimately, the team knew they needed a clean slate, so Clarus brought in a senior developer with experience in both PHP and Elixir. Frustrated after multiple failed attempts to refactor the PHP code, he rewrote Clarus’ entire calculation engine over a weekend to impressive results. The same calculations that took 30+ seconds with PHP now took mere milliseconds.
While other tech stacks could have offered the same performance improvement for Clarus’ calculation engine, Elixir came with the added benefit of paving the way to make its product development team small but highly responsive. With Phoenix LiveView, Clarus could focus on a smaller team of engineers covering both server-side and front-end needs, all in Elixir.
Rebuilding Smarter, Not Just Faster
Rewriting an application is never a small decision. It takes time, investment, and trust from leadership. The team spent about six months rebuilding the platform using Elixir, Phoenix, and LiveView. The end result was a healthy code base at feature parity with the original app, but more performant, stable, and flexible, receiving much-needed new features easily.
The rewrite enabled Clarus to rethink and streamline critical features. The calculation engine, for example, now returns results in a fraction of a second. The LiveView front end produced a more responsive user interface that was easier to use and less bug-prone than the previous version.
With those improvements and a healthy codebase in hand, Clarus’ team was able to focus on developing the digital product development practices that would help them maintain and grow Clarus’ app sustainably.
Unlocking Business Value
After relaunching on the new platform, Clarus saw immediate improvements. Internal processes were smoother. New studies for clients could be run with minimal effort. The engineering team had fewer support requests and more time to focus on feature development.
The rewrite also helped Clarus respond more quickly to client and partner needs. When the app ran on PHP, linking studies to the right client was a difficult task. With Elixir, however, Clarus’ partner program not only ran more smoothly, but the solid foundation made it possible to add new features that resonated with CPA firms and channel partners.
Ushering in a solid foundation with Elixir set the stage for that level of responsiveness. Using a single tech stack for Clarus’ entire app eliminated the roadblocks inherent to the previous iteration and replaced it with a healthy codebase. That, in turn, allowed the product development team to move quickly: When customers voiced a specific need, Clarus’ team was able to quickly respond and deliver value.
Setting the Stage for Acquisition
When it came time to engage with a potential acquisition partner, the ability to adapt quickly to changing market needs was foundational to nurturing that relationship. Buyers needed to know they were investing in a product that was reliable, secure, and built to scale. Elixir helped Clarus demonstrate just that.
The rewritten application passed technical due diligence with minimal friction. Its clean architecture and ability to support a component-based model aligned well with the acquiring company’s goals. Without the rewrite, Clarus would have faced more risk—slower performance, higher maintenance costs, and missed opportunities to deliver critical features on time.
Ultimately, Elixir helped Clarus maintain a strong product with fewer resources while also making it easier to support the evolving needs of the business. That stability and agility were key assets during the acquisition.
Conclusion
Elixir isn’t a magic wand, but when used strategically, it can be the foundation for scalable, adaptable custom app development. For Clarus R+D, it turned a sluggish, hard-to-maintain platform into one that supported growth, enabled faster iteration, and set the stage for a successful acquisition.
