Arda Erzin

Berlin

I keep large codebases easy to work in.

Now

For the last two years I’ve been the principal author of the web frontend at Agenta, an open-source platform for building and evaluating LLM applications. Before that I led a four-engineer team at Medbelle through a Next.js 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 use it the way I build it: the harness matters more than the prompt.

Work

2024 — 2026

Agenta

Lead Product Engineer · open-source LLM engineering platform · Berlin

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

  • I carved ten shared workspace packages out of the monolithic app so desktop and a new mobile client render one definition, delivered as a numbered stack of small reviewable PRs.
  • I built the agent chat surface: token streaming, inline tool calls, human‑in‑the‑loop approval.
2021 — 2024

Medbelle

Engineering Team Lead · digital healthcare · Berlin

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

2013 — 2020

Before that

Berlin · Istanbul

I built and ran DotLab, my own e-commerce company in Berlin, for four years, and co-founded Overthink, an MVP studio in Istanbul. I led iOS at Synnc, a social music-listening platform, and product-managed at the Startup Kitchen venture builder.