Full-stack developer based in Colombia. I build and run the software a private security company depends on every day: a mobile app published on Google Play (ready for the App Store), the APIs behind it, web platforms for HR, billing and suppliers, AI agents that run on-premise, and the Windows/SQL Server infrastructure they all live on.
I like taking legacy systems that "just work" and making them secure, observable and deployable with one command, without stopping the business.
📱 Mobile React Native · Expo · offline-first sync · GPS/geofencing · camera/QR/NFC · FCM · Play Store / App Store
🧩 Backend Node.js · Express · TypeScript · Python · FastAPI · REST · WebSockets
🟦 .NET VB.NET · C# · ASP.NET WebForms · ASP.NET Core · .NET Framework 4.8 / .NET 8 · ADO.NET · IIS
🗄️ Data SQL Server · T-SQL · Prisma · Drizzle · SQLite · query tuning · backup/restore · cross-server migrations
🤖 AI Local LLMs with Ollama · OCR (Tesseract, PyMuPDF) · grounded generation · document extraction
🛠️ Ops IIS · NSSM services · PowerShell automation · Git-based deployments · CI (GitHub Actions, Codemagic)
🔐 Security Hash migrations (PBKDF2) · secrets out of source · signed links · webhook signatures · least privilege
- Field operations mobile app (React Native). Shifts, geofenced check-in with selfie validation, patrol rounds with NFC/QR, incident reports, payroll self-service and push notifications. It works offline with a durable sync queue and is published on Google Play, with the iOS build ready for the App Store.
- REST API for the app (Node.js + SQL Server on IIS). More than 20 business modules, JWT, scheduled jobs, PDF generation and structured per-module logs with request IDs.
- WhatsApp helpdesk (Express, Prisma, Socket.IO, React). A bot menu that routes customers to several departments, live agent inbox, business hours, and dashboards.
- On-premise AI agents (Python, FastAPI, Ollama, OCR). Supplier invoice intake, accounting exports and billing files. They replaced hours of manual data entry and keep the data on the company's servers.
- LLM-written executive reports for clients, with every figure validated against the database.
- Legacy modernization. I moved hard-coded credentials into protected configuration, migrated plain-text passwords to salted hashes without forced resets, rewrote classic ASP endpoints, and added dev/prod profiles.
- Infrastructure migration. I moved the apps and databases to a new server (SQL Server 2016 → 2022, new IIS layout), with resumable attachment copies, schema comparison and scripted, versioned deployments with rollback.
These are clean-room portfolio versions of the patterns behind that work. They are written from scratch, use synthetic data, and come with tests and CI.
| Repository | Stack | Highlights |
|---|---|---|
| fieldops-offline-mobile | React Native · Expo · TypeScript | Durable offline outbox (idempotency keys, per-entity ordering, backoff with jitter, crash recovery), single-flight token refresh, accuracy-aware geofencing. 41 tests. |
| node-mssql-api | Node.js · TypeScript · SQL Server · IIS | Mobile-app backend: injection-proof SQL template, migrations, one-open-shift index, refresh-token rotation, cron jobs with a distributed lock, FCM push, email, PDF reports, per-module logs. Integration tests run on a real SQL Server in CI. |
| whatsapp-helpdesk | Node · Express · Socket.IO · Drizzle · React · Tailwind | Bot menu editor, least-loaded agent routing, queues, business hours, HMAC-verified webhooks, real-time inbox and dashboard. 28 tests. |
| invoice-ai-extractor | Python · FastAPI · Tesseract · Ollama | Rules first, then a grounded local LLM. Colombian NIT check-digit validation, OCR fallback, accuracy gate in CI. 41 tests. |
| llm-report-writer | Python · Ollama · ReportLab | Executive PDF reports where the LLM writes and a guard rejects invented numbers, overlong paragraphs and repeated closings. |
| supplier-portal-webforms-vb | VB.NET · ASP.NET WebForms · .NET Framework 4.8 · SQL Server | Supplier portal in VB.NET: parameterized ADO.NET, PBKDF2 with legacy upgrade, CSRF protection, signed certificate links, least-privilege SQL. CI builds on Windows and runs an IIS Express smoke test. 28 tests. |
| aspnet-legacy-auth-migration | .NET 8 · C# · SQL Server | From plain-text passwords to PBKDF2 with transparent upgrade on login, HMAC-signed expiring links, lockout with backoff. 18 tests. |
| windows-server-ops-toolkit | PowerShell · IIS · SQL Server | Versioned zero-downtime IIS releases with auto-rollback, NSSM service updates from Git, resumable migrations, schema diff. Pester tests. |
| Repository | Stack | What it is |
|---|---|---|
| MercadoAgentes | Java · JADE · Swing | Multi-agent marketplace: shops and buyers negotiate with FIPA Contract Net, concurrent negotiations and automatic retries. Built for my Multi-Agent Systems course at UNIR. JUnit tests and CI. |
| front-gestion-deportiva | Vue 3 · Vite · Vuetify | Sports school management UI (coaches, students, classes, schedules, events). Team project, I did the redesign and the forms. |
| person-crud-api-spring-boot + person-crud-vue | Spring Boot · PostgreSQL · Vue 2 | One of my first full-stack apps (2023): REST API and its frontend, later cleaned up with tests, CI and config through environment variables. |
📫 jh.deivy@gmail.com · 💼 LinkedIn