Juan M.

Senior full-stack engineer (10 years) building SaaS products and AI features with Next.js, TypeScript, Supabase and Stripe. Top Rated Plus · 100% Job Success · Fluent English · Argentina (UTC-3), working hours overlap with the US and Europe. WHAT I BUILD • SaaS web apps end to end: auth, multi-tenant data with Row-Level Security, Stripe subscriptions and billing portals, dashboards. • AI features that are safe in production: Claude / OpenAI agents with tools, human approval for risky actions, tests and evals. • WhatsApp and chat bots on the official APIs (WhatsApp Cloud API, Telegram), with human takeover. • Chrome extensions (Manifest V3): content scripts, popups, storage, automation of internal workflows. • Mobile apps with React Native (iOS + Android from one codebase), including offline sync. • Enterprise front-ends in Angular and React for regulated industries like insurance. PROOF • Turned a field-service ERP into a multi-tenant SaaS on Supabase + Stripe. I wrote the tenant-isolation migration (Row-Level Security, existing data moved in as the first tenant) and co-built Stripe Checkout, webhooks and self-serve sign-up. • Built AI quote-PDF import with OpenAI for a modular construction ERP (France): PDFs become structured, reviewable data instead of manual re-typing. • Top contributor to the Next.js rewrite of a live B2B fitness SaaS: 503 of ~1,184 commits. I also work on its React Native app (offline workouts, messaging notifications). • Built a WhatsApp AI booking agent on Claude + Supabase that can only offer real time slots, tested against 20 scripted conversations including prompt-injection attempts. • 5 years building insurance products with React at an InsureTech company. Before that, 5 years maintaining the core billing system of a major regional brewery. • Clients say: "delivered exactly what I needed on time… went above and beyond" and "didn't stop until it was finished to my complete satisfaction." STACK Next.js · React · TypeScript · Node.js · NestJS · Supabase · PostgreSQL · Stripe · Claude API · OpenAI API · MCP · React Native · Angular · Vue/Nuxt · Tailwind · REST/GraphQL HOW I WORK 1. Short call or written brief to map the real workflow and agree on scope. 2. A clear plan with milestones; you get a demo or short video at each step. 3. Clean, typed code with tests where it matters, plus a README your team can run without me. 4. Daily async updates in English or Spanish, and real-time overlap with US/EU hours. Have a SaaS, AI feature or extension in mind? Send me a message with what you're building and your timeline, and I'll reply with a concrete plan.