Jay Koh —
I help FinTech and SaaS teams integrate payment gateways, build resilient backends, and hit 99.9% SLA — so you can focus on product.
What I Do
End-to-end engineering across the full stack, from payment infrastructure to production deployment.
Connect your product to any payment provider, fast. I've wired up 14+ gateways so your transactions flow without downtime or data loss.
High-throughput systems in Go, Ruby, Python, and Java. I build the backend that handles your peak traffic without breaking a sweat.
CI/CD, Docker, monitoring stacks (Grafana/ELK/Zabbix), and cloud architecture. I keep your systems at 99.9% uptime so your team sleeps well.
Clean, responsive interfaces and dashboards that make complex data easy to act on. From admin panels to customer-facing portals.
Career
Process
A straightforward process from first call to production deploy.
We talk about your stack, pain points, and goals. I ask the hard questions upfront so there are no surprises later.
You get a clear scope, timeline, and architecture plan. No vague estimates — just concrete deliverables with milestones.
I build iteratively with weekly check-ins, deploy to production, and hand off clean documentation. You own everything.
Domains
Insights
Practical lessons from building payment systems in production.
Image hardening, secrets management, network isolation, and runtime security — lessons from three FinTech deployments.
Read article →FX rate mismatches, correspondent bank fees, settlement timing gaps, and building a reliable recon pipeline.
Read article →Frictionless auth flows, SCA exemptions, soft declines, and the gotchas nobody warns you about when integrating 3DS2.
Read article →Token bucket vs sliding window, Redis Lua scripts for distributed limiting, and the middleware pattern that saved us at 3am.
Read article →The two-layer authorization system, tokenization, PCI compliance levels, and five things I learned the hard way.
Read article →Stripe, Adyen, Braintree, and Checkout.com — honest breakdown from integrating 14+ gateways in production.
Read article →Why Work With Me
I spent years building payment infrastructure inside enterprise teams — integrating Visa APIs, wiring up 14+ gateways, and keeping systems at 99.9% uptime. Now I bring that same engineering rigor to independent consulting. You get senior-level work without the overhead of a full team.
"Currently building my freelance portfolio and offering competitive rates for early clients. Same enterprise-grade work — better value for you."
Contact
Have a project in mind or need a reliable engineer for your team? I'm open to full-time roles, contract work, and consulting engagements.