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 designed how a running agent asks its user for things mid-run: typed forms with accept and decline instead of free text, which cuts input errors on the user's side and gives the agent structured interactions without planning every one in advance. The forms speak the MCP elicitation dialect, so connected tools can request typed input too.
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