Full Stack Engineer & AI Engineer
Kem John Mantos — Full Stack Engineer and AI Engineer — websites, web apps, mobile, and the payment systems behind them, built with multi-agent workflows I design myself. Nine years shipping production software.
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.
The AI engineering is what makes it fast. I don't just prompt a chatbot — I architect multi-agent pipelines: for one product, eight role-scoped agents (frontend, backend, Swift, QA, code review, security review) with defined boundaries and handoffs, so generated code clears adversarial review before it reaches me. I've deployed MCP servers and standardised the spec-driven workflow my teams now use.
That's how four production products shipped in under two months — across native macOS, Git internals, device management, and web. The difference from a vibe coder: I set the architecture, data models, and security decisions; the AI writes to that design, it never sets it. Every line is reviewed and tested against payment-system standards.
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.
Multi-agent development pipelines I design — not prompts typed into a chatbot.
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.
Repo LaneA 12 MB native git client for macOS and Windows.
Stage by the chunk or the line, read a commit graph drawn properly, merge stacked pull requests, and recover the work git says is gone. Built solo in under two weeks, with a device-bound licensing system — signed license files and an activation-code flow. Currently in closed testing on both platforms.
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.
A 12 MB native Git client for macOS and Windows — chunk- and line-level staging, a commit graph drawn properly, stacked pull requests, and recovery for work Git says is gone. Ships with a device-bound licensing system: signed license files, an activation-code flow, and license-gated distribution builds.
Visit Repo LaneInternal MDM for company-owned hardware — device enrolment, policy distribution, and fleet visibility, built to replace a licensed third-party tool.
Company-wide Markdown viewer for internal documentation — searchable, versioned, and shipped in a single day from spec to deployed.
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.