Complex things, built simple.

    I’m Mateusz Sowiński, a software engineer at S&P Global. I build resilient .NET back-ends and modern React front-ends, and I write about the craft on my blog.

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    2018Gdańsk University of TechnologyComputer science: algorithms, team projects

    2019JMB LabFull-stack developer: C#, .NET, SQL, Angular

    2024S&P GlobalSoftware engineer: C#, back-end at scale, cloud

    2025Writing in publicA blog in three series: Serilog, hosting, AI coding

    2026Working with AI agentsTen apps in one month: Claude Code, Codex, Raspberry Pi

    20182019202420252026
    2026

    Ten apps in one month

    Claude Code builds, Codex reviews, and a 2016 Raspberry Pi keeps seven of them running.

    AI wrote almost all the code. Knowing what runs underneath kept my data private, my bills low and my numbers right.

    • Fin StatsInvestment dashboard for Poland, computed only in the browser.
    • House BuilderFloor-plan editor with a 3D view and Polish building rules.
    • RPI ManagerAI limits, costs, deploys and Raspberry Pi health in one place.
    • FPL ScoutFantasy Premier League advisor that shows where several models agree.
    • Car StatsCar logbook fed by photos of the dashboard and the pump.
    • ReportsMarket reports written on a schedule, each fact with its source.
    2025

    Writing in public

    24 posts in 3 series, and counting.

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    1. Torn brown wrapping paper revealing the A and I keys of a laptop keyboardI Pay $120 for Claude and Use $7,000 at API Prices. Why?
    2. A railway track splitting in two, with an old sign reading OPUS 5.5 by the left branch and FABLE 5.2 by the right oneClaude Fable 5.2 vs Opus 5.5: It Wins. Should You Switch?
    3. A hand bringing a hammer down on a glowing bar of steel on an anvil, with sparks flying10 Apps in a Month With AI: Code Got Cheap, Judgment Didn't
    1. 2024

      S&P Global

      Software engineer

      “Even more exciting than I expected.”

      A far larger scale and a wider set of problems. Back-end work in C#, where I lean on what I know and still learn parts of it from scratch.

    2. 2019

      JMB Lab

      Full-stack developer

      “I’d choose it again without hesitation.”

      My first job and the best possible start. Harder tasks every month, and a manager who taught me more in one year than three years of lectures did.

    3. 2018

      Gdańsk University of Technology

      Computer science

      “The best studies I ever had.”

      Five years of algorithms, exams and team projects, with people I still call friends. It gave me the foundation to become an engineer.

      The whole story

    4. Two games, for when you need a break

      SnakeThe arcade classic. Eat, grow, and dodge your own tail as it speeds up.
      Rock · Paper · ScissorsAn elimination tournament with friends, or solo against the computer.

    You’re in the right place.

    Whether you’re looking for a dedicated developer or just share a passion for tech, write to me.

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