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Deniz Yıldırım

@deniz_cto

Co-founder & CTO of a 12-person B2B SaaS in Berlin (Kreuzberg, obviously). TypeScript, Postgres, hiring. Yes we are hiring. No we cannot sponsor visas yet 😅

  • Berlin, Germany
  • German · Turkish · English
  • Joined Aug 2026
  • Last posted Sep 10, 2026

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Everything this author has published.

Deniz Yıldırım1.2K
t/ai_hype_check3 min

We let AI write our tests for a quarter. Coverage went up, confidence did not

Quick context: 12 people, 5 engineers including me, TypeScript monorepo, Postgres, Vitest. In Q2 we had a mandate (from me, honestly 😅) to "use AI to fix our test debt". Coverage was 41% and our investors' tech DD person had made a face. What we did Every engineer used an AI assistant to generate tests for untested modules, about 30 minutes a day. Rule: tests must pass and get reviewed in the PR like any other…

9

  • Siobhan O'Rourke
    'The test enshrines the bug' is the sentence. I've been trying to explain this to my director for months. Coverage measures execution, not verification. Mutation score is the honest number, so glad you tracked it.
    1 reply
Deniz Yıldırım590
t/bootstrapped_and_broke3 min

Runway math for a 12 person Berlin startup: '27 months' is a lie we tell ourselves

Every founder I know says "we have two years of runway". Honestly, most of them are counting wrong. We were. Here is our real math, slightly rounded, embarrassing parts included 😅 The naive version Bank: €2.1M (seed, closed last year) Monthly costs: about €115k Revenue: €38k MRR Net burn: €77k a month Runway: 2.1M / 77k = 27 months 🎉 Where the €115k actually goes Gross salaries, 12 people: €78k Employer social…

14

  • Hannah Weiss
    Small correction to an otherwise accurate breakdown: the employer share is roughly 20 to 21%, yes, but it is capped at the contribution ceilings, so for your senior people above the ceiling it is a lower percentage. Your €16k is probably a little high. The Steuerberater would know.
    1 reply
  • Guillaume Mercier
    In France this would be three meetings with the CSE and a lawyer before anything happens. You Germans are Americans with a notary 😏 bref, good post, the SaaS audit is a real lesson

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