I’m Gerwin, a software engineer who builds and ships complete products, from backend to infrastructure. This site is where I share my work and ideas. Read more about me, or scroll down to get in touch.
Software Engineer
Gerwin Kuijntjes
Software engineer who builds and ships complete products, from backend to infrastructure.
NL / EN
About
Featured projects
PersonalHours: A Time Tracking App for My Mother
An Android app that keeps track of the hours my mother works at a handful of private households and what they add up to. She noted it in her diary and typed it into a spreadsheet at the end of the month; the app turns that around and only asks her to confirm what it already knows.
SaaSVessia: Ship Administration Without the Double Entry
A complete administration platform for inland shipping skippers: trips, time charters, invoices, custom onboard documents, gasoil and measurements in one place. Built in close collaboration with my brother, an inland skipper himself, because the Excel templates I made for him years ago never really solved the double data entry. Built on my own Slicekit template and live on vessia.app within weeks.
SaaSSendScope: Monitoring and Alerting for AWS SES
An all-in-one platform to monitor AWS SES deliverability and receive automatic alerts when something unusual happens. Built after a leaked AWS key got our SES account suspended, blocking all transactional emails, because AWS itself has no workable solution for proactive monitoring.
SaaSSlicekit: A Full-Stack .NET + React SaaS Template You Own
A production-grade SaaS template that ships the boring 80% already built: an event-driven .NET 10 API (vertical slices, DDD, CQRS, messaging) paired with a typed React 19 SPA, plus an Astro marketing site. Passkeys, TOTP, OAuth, granular permissions, a finished admin panel, Stripe billing, a hash-chained audit trail, full observability and CI included. Built because I kept rebuilding the same foundation on every project, and sold once under a commercial license so you own the code.
PersonalGeldhoek: Privacy-First Calculators for Dutch Money Questions
A free, privacy-first suite of Dutch financial calculators in one place: net salary, maximum mortgage, allowances, savings, and box 3. Every calculation runs client-side, with privacy-friendly analytics that only shows statistics and never your inputs, built on a single source of truth for fiscal figures that is verified each year against official sources.
PersonalGaren Collectie: A Thread Inventory App for My Mother
An Android app that helps my mother keep track of her Gütermann sewing thread collection. It pairs a full catalogue of all 400 thread colours, scraped from a Dutch haberdashery, with a personal inventory so she always knows which colours she already owns before buying more.
SaaSStaticForm: Form Backend With Spam Filtering and Full Observability
A SaaS platform that turns any HTML form into a reliable submission pipeline, with 10+ spam checks, complete action logging, failure alerts, and a flat monthly fee that never charges per submission. Built originally to stop rebuilding the same form backend for every client project; now used by developers and agencies managing forms across multiple sites.
PersonalP1 Meter Monitor: Automated Energy Tracking and Reporting
A Dockerized Python service that collects readings from a Dutch P1 smart meter, stores them in a QuestDB time-series database, and emails periodic consumption reports including solar export tracking and month-over-month comparisons.
Recent posts
TechnicalSwitching proxies in .NET without creating a new HttpClient every time
A practical way to choose a different proxy per request in .NET, without named clients or changing the handler after startup.
AI Is a Car, Not a Bike: How to Actually Use It as a Developer
Why AI coding is a skill, not a threat, and how thinking of it as a car instead of a bike makes you far more effective
How to Fix Procrastination for Good: A Scientific Approach
Discover how to overcome procrastination by managing activation energy and entering flow, based on principles from physics and chemistry
Get in touch
Let's Connect
Have a question, useful feedback or an idea we could work on together? I don't use social media, so contact me through one of the options below.