Software Engineer
Aaron Metzelaar
I'm a software engineer who likes building things that feel simple on the outside and solid underneath. My work combines product thinking, frontend engineering, automation, and AI tooling, with a focus on turning unclear ideas into practical solutions people actually enjoy using. I'm curious, hands-on, and collaborative, and I enjoy helping teams work smarter as much as I enjoy building the product itself. Off the clock, I play football, organise events with friends, and I'm always up for a good specialty coffee.
Experience
MatchWornShirt · Frontend Engineer
2023 – PresentWork across the public marketplace, mobile app, and internal admin tools as a T‑shaped engineer: deep in frontend and product experience, with broad involvement across backend-adjacent integrations, DevOps/CI workflows, automation, internal AI tooling, and developer productivity.
Frontend & product engineering
- Built and maintained customer-facing and internal features across web, mobile app, and admin tooling
- Improved frontend maintainability through shared composables, reusable implementation patterns, refactoring, and documentation
- Designed product-critical workflows across CMS-driven content, operational tooling, translation flows, and cross-platform frontend logic
- Delivered solutions through cross-functional collaboration with product, design, marketing, support, and engineering
AI tooling & developer productivity
- Designed and maintained the internal AI agent ecosystem for frontend and mobile engineering
- Built reusable AI-assisted workflows for codebase context, advanced reviews, worktrees, documentation, and engineering automation
- Improved engineering consistency across quality, documentation, reviews, and internal processes
Localisation & content infrastructure
- Revived a deadlocked translation project and turned it into a scalable multilingual publishing system
- Replaced a blocked backend-first approach with a practical localisation strategy across CMS content, UI copy, validation, and release workflows
- Reduced manual translation overhead and release risk with cleaner content structures, automated checks, and developer-friendly workflows
- Enabled reliable publishing across 12 languages for multiple products
Payments, checkout & business impact
- Introduced Klarna across web and app, establishing reusable payment logic for company products
- Improved checkout visibility and consistency, reducing unpaid orders by 40%
- Validated placement decisions through A/B testing, ad hoc analysis, and product research, prioritising high-impact implementation over unnecessary scope
Engineering quality & team enablement
- Top reviewer and contributor across web, app, and admin codebases
- Improved developer experience by standardising workflows, AI workflow guidance, documentation, and reusable engineering practices
- Coached engineers through presentations and hands-on sessions on code quality, workflow adoption, and safe tool usage
Highlighted projects
- Internal AI agent ecosystem: Increased AI co-authored PR adoption from 5% to 35% by turning AI usage into structured team workflows
- Klarna payment integration: Introduced Klarna across web and app, contributing to 40% fewer unpaid orders and an 8% higher bid placement rate
- Translation & localisation workflow: Revived a stalled translation project and scaled publishing across 12 languages, 154,500+ CMS words, and 11,500+ strings
- Frontend architecture: Designed reusable frontend solutions for complex product experiences, including shared 360° image logic, contributing to 60% higher user engagement
Education
BSc Computer Science
University of Amsterdam · 2024Thesis: Projection-Based Interaction using Tangible Objects. A Mixed Reality framework I built in Unity that uses a camera and projector to track real objects.