Arda Erzin — frontend engineer, Berlin

Now

For the last two years I’ve owned the frontend’s technical direction at Agenta and led its frontend team. Agenta is an open-source platform for building and evaluating LLM applications, and since mid-2026 an agent builder. Before that I led the engineering team at Medbelle through a framework migration, a monorepo consolidation and a design-system replacement, none of which were allowed to stop delivery. I’ve been writing React since 2015.

I’ve spent my career in startups, twice as a founder, and I started out on the product side, testing MVPs at a venture builder before I wrote production code. The habit that survived the switch is asking what a feature is for before building it; unbuilt features are the easiest ones to maintain. When something matters I take it end to end.

The opinion

Never write the second copy.

If two surfaces need the same thing, I extract it into a shared package, stylesheet and tokens included. A component extracted without its styles renders wrong, and nobody catches it in review. I don’t trust my eyes on that kind of change, so I diff the generated CSS instead.

With AI

I build LLM tooling for a living, and I build with it daily. What made agents useful on my team was giving them a defined surface to work against: a skill written per extracted package, and test suites shaped to what each package needs.

Work

2024 — 2026

Agenta

Lead Product Engineer · open-source LLM engineering platform, now an agent builder · Berlin

I owned the frontend’s technical direction and led the frontend team: the architecture, the library choices, the shared package layer.

I rebuilt the prompt playground in my first two months, the interaction design as well as the code. It had stuttered on one prompt with a few test cases, and came out running several prompts across many test cases side by side. Prompt management, evaluations and testsets followed.
When the product pivoted to an agent builder, I built the surfaces it runs on: composing an agent from skills, MCP tools and a model, a streaming chat to drive it, approval gates on consequential actions, and scheduled runs.
I carved ten shared workspace packages out of the monolithic app so desktop and a new mobile client can render one definition, delivered as a numbered stack of small reviewable PRs. Most of that layer is merged, the rest in review.

2021 — 2024

Medbelle

Engineering Team Lead · digital healthcare · Berlin

I stepped into the lead role when the CTO moved into product, and ran the engineering team owning three patient-facing applications and the marketing site.

I ran the consolidation into a monorepo, the migration off a legacy styled-components design system to Tailwind, and the framework migration that brought in middleware-based patterns. None of it paused feature work.
I worked the full stack on those applications, Django and Graphene included.

2016 — 2021

SRH Hochschule Berlin

Startup Lab, part-time · hands-on entrepreneurship · Berlin

I instructed and mentored every semester from graduating until I joined Medbelle: business-model and hypothesis validation, build-measure-learn loops.

2013 — 2020

Before that

Berlin · Seelze · Istanbul

I co-founded DotLab, an e-commerce studio in Berlin, and ran it for three and a half years. At Wintech PS I ran InnHof, an intrapreneurship project inside an international manufacturing firm, and steered its pivot from a physical innovation centre to a digital one when the parent company halted the building programme. I also co-founded Overthink, an MVP studio in Berlin, whose own product was Synnc, a social music-listening platform I led the iOS app for. Earlier I product-managed at the Startup Kitchen venture builder in Istanbul.

Now