Full Stack Engineer
Kem John Mantos — Full Stack Engineer — websites, web apps, mobile, and the payment systems behind them. Nine years shipping production software that businesses run on.
Positioning
I build complete products for businesses — marketing sites that convert, web apps, mobile apps, and the backends underneath them. Next.js and React up front, Kotlin and Spring Boot below, PostgreSQL and AWS at the bottom. Whatever your business needs on a screen, I can build it end to end.
What sets the standard is where I learned the craft: nine years on the hardest part of the stack — payment systems, Apple and Google Wallet platforms, and infrastructure where a bug costs real money. When your website is built by someone banks-adjacent products trust with transactions, 'it just works' is the baseline, not the goal.
AI-augmented development is what makes it fast: I ship whole products — web, mobile, native macOS — at startup pace. The difference from a vibe coder: every line gets reviewed, tested, and held to payment-system standards. AI is my accelerator, not my architect.
What I do
Business sites and web products that are fast, findable, and built to convert.
One product, on every screen your customers actually use.
The specialty: when your product touches money, this is my home turf.
High-availability infrastructure with the observability to prove it.
Release process across thirty-plus engineers and two countries.
Proof below —
keep scrolling.
Case studies
Deep dives into the hardest systems I've shipped — problem → constraints → architecture → outcome. Every website and app I build gets this same rigor.
Also shipped
Menu bar agent with watchdog architecture in Swift 5.10 / SwiftUI — real-time screen streaming via ScreenCaptureKit, Keychain-backed credentials, SSE push, and policy-driven automation.
Full-featured Git client for macOS, built entirely in Swift — staging, branching, history, and diffs in a fast native interface. Ships with a device-bound licensing system: signed license files, an activation-code flow, and license-gated distribution builds.
Cross-channel transaction tracking with automatic failure handling and dispute resolution — the machinery that keeps a multi-channel ledger honest without human sweeps.
Org-wide scanning rollout — StepSecurity, CodeQL, Trivy, Gitleaks, Semgrep, Legitify — wired into the default CI path, plus a GitHub MCP server for enterprise integration.
Track record
Vauldex Technologies Inc.·Mar 2026 — Present — 6 months
Vauldex Technologies Inc.·Mar 2023 — Present — 3+ years
Vauldex Technologies Inc.·Jul 2018 — Feb 2023 — 4 yrs 8 mos
Vauldex Technologies Inc.·Nov 2016 — Jun 2018 — 1 yr 8 mos
City Savings Bank·Jun 2015 — Aug 2015 — 3 months
University of Cebu·2012 — 2016
Engagements
A fast, modern site that makes your business look like it means it — design to launch, SEO-ready, easy to update, and built to turn visitors into customers.
Idea to production across the whole stack — AI-accelerated velocity with nine years of engineering discipline behind every merge. Fast to ship, built to last.
Stripe checkout, subscriptions, webhook debugging, Apple & Google Wallet passes — the money parts of your product, done by someone who does them daily.
A senior engineer on call: fixes, new features, performance work, and honest advice — without the overhead of a hire.