Jarle Mathiesen
Senior software engineer · Oslo, Norway
I’m a senior software engineer in Oslo. I do my best work in product teams, close to the users and the problem, taking ideas all the way to something people rely on every day.
For eight years I’ve built systems where the numbers have to be right: pension premium calculation for Norway’s largest public pension provider, and reporting and invoicing at Posten Bring.
I use AI to raise both the quality and the scope of what I build, and I’ve shipped products with AI at the core: SummYT, a video summarizer with more than 200,000 registered users, and an assistant that analyses Posten Bring customers’ reports and invoices.
Now
Senior consultant at Knowit, on the Analytics team at Posten Bring. Our department owns Mybring, the self-service platform for Posten Bring’s business customers, and my team works on its reporting and invoicing. Outside work I maintain open-source projects around AdonisJS.
How I work
Product first
I care about what the product does for the people using it, not just the code. My best work has come from autonomous product teams that own a problem end to end.
Built to be right
Pensions, invoices and reports leave no room for “roughly correct”. Domain-driven design, good tests and continuous integration let a team ship often without fear.
AI as leverage
I follow the field closely and share what I learn, including through internal workshops. Coding agents like Claude and Codex let me take on more and raise the bar on quality, while the team keeps its understanding of the system. I wrote about why that matters in Cognitive Debt. Read it.
Selected work
SummYT
AI summaries of YouTube videos, as a web app and a browser extension. Launched in 2023 as YouTube Summarized. Full stack, built and run by me. 200,000+ registered users.
Mybring AI assistant
An assistant that helps Mybring’s business customers work with their reports and invoices. Domain-specific tools let it run aggregations and analysis on their actual data, not just answer questions.
Matstack
react-adonisjs: full-stack React Router apps on AdonisJS 6, with ORM, auth and dependency injection built in. 55+ GitHub stars.
Talks
Your Service Layer Is a Mess (Here’s a Simple Fix)
Service layer patterns for backend applications. The fix ships as installable agent skills alongside the slides.
Experience
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Knowit · Posten Bring
Senior consultant
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SummYT
Founder
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Bouvet · Statens pensjonskasse
IT consultant
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RISE Research Institutes of Sweden
Software developer
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Linköping University
MSc, Computer Engineering
Writing
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Cognitive Debt
If agents write more of our systems, what happens to the human understanding required to operate, change, and trust those systems over time?
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Understanding Email Under the Hood Guide
A developer's guide to how email actually works, from MIME and MX records to SMTP, SPF, DKIM, and DMARC.