Welcome
Hi, I'm jguillaumesio, a full-stack contractor based in Paris, working 100% remote. I help SaaS teams ship the parts they can't afford to get wrong: payments/billing integration and AI agents in production. This blog is where I write about what I ship.
Welcome đź‘‹
I’m jguillaumesio, a full-stack contractor based in Paris, working 100% remote. I help SaaS teams ship the parts they can’t afford to get wrong: payments/billing integration and AI agents in production, under a full-stack umbrella.
What this blog is
A working notebook, not a content funnel. Every article here comes from a real problem I shipped in production for a real client. No “Hello World”, no “Top 10 Tips” listicles. Just honest write-ups of what broke, what was learned, and what the solution actually looked like.
If a post here saves you three hours of debugging, or helps you avoid a bad migration, the work is doing its job.
What I do for work
Two specialty lanes (see the services page for the full picture):
- Payments / billing integration, Stripe migrations with zero downtime, multi-provider checkout, reconciliation, loyalty, VAT/MOSS.
- AI agents in production, agentic coding pipelines, RAG over codebases, Mastra-based agent orchestration, and the boring but critical production concerns (cost, latency, evaluation, human-in-the-loop).
- Full-stack SaaS, the umbrella. React / React Native / Node / TypeScript / Laravel. I can own a product end-to-end.
How to read this blog
- The articles index sorts by recency
- The about page is the short version of who I am
- The case studies are anonymized proof-of-work for the engagements I’ve taken on
- The services page is what I do, for whom, and how to book a call
More articles coming soon. If you’d like to work together, the fastest way is the book a call link.