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Dennis O. Arroyo Rivera

Senior Software Engineer

Engineer building AI-powered and full-stack systems on .NET and Azure.

About

I'm a Senior Associate Software Engineer at Xtillion, an AI and data engineering consultancy. My first project was an internal platform the operations and HR teams use every day for timesheets, time off, approvals, and staffing. I worked across the full stack in TypeScript, Next.js, GraphQL, and PostgreSQL. I've since moved on to client work for a large pharmacy benefit manager, using .NET, Azure, and AI agents to automate documentation for their Medication Therapy Management process.

Before Xtillion, I did contract work with Snac PR, where I designed and shipped a user access-request and identity-provisioning microservice for the PR Department of Justice. I also spent over a year owning Bioresults (HL7 lab-result ingestion) and contributing across BioPortal, Puerto Rico's public health surveillance platform, on a .NET 10 and Angular stack. 6+ years of industry work behind it.

Before this stretch, I spent two years on doctoral research in cybersecurity, looking at confidentiality, integrity, and availability tradeoffs in Internet of Medical Things devices. I finished a graduate degree at Polytechnic University of Puerto Rico. The tension between security and usability from that research still shows up in my work today.

A few years back I automated a nightly job at the Puerto Rico judiciary, so staff no longer had to come in on Saturdays to process protection orders. I'm still proudest of that one.

Experience

  1. Aug 2026 — Present

    Senior Associate Software Engineer · Xtillion

    Client work for a large pharmacy benefit manager, building an ASP.NET Core endpoint that uses an MCP server and an AI agent to generate the documentation required for Medication Therapy Management (MTM). It automates the most tedious step of the process so people can spend that time on other work. Before that, built and maintained the company's internal platform for timesheets, time off, approvals, and staffing, moving employment history to an event-based model, retiring eight legacy tables, and fixing timezone bugs that shifted Puerto Rico users' dates by a day.

    • .NET 8
    • C#
    • OpenAI
    • MCP
    • Azure
    • TypeScript
    • Next.js
    • PostgreSQL
  2. Jan 2026 — Jul 2026

    Senior Software Engineer (Contract) · Puerto Rico Department of Health

    Owned Bioresults (HL7 lab-result ingestion) and contributed across BioPortal, Puerto Rico's health surveillance platform. Worked directly with labs across the island and mentored mid-level engineers through planning and review.

    • .NET 10
    • .NET Aspire
    • C#
    • Angular
    • HL7 v2.5.1
    • Azure
  3. Nov 2025 — Oct 2026

    Senior Software Engineer (Contract) · Snac PR

    Designed and shipped the RCI access-request and identity-provisioning microservice for the PR Department of Justice, which now runs in production. It handles access management and connects to centralized identity services across government systems.

    • .NET 10
    • Entity Framework Core
    • Angular 21
    • JWT
    • Active Directory
  4. Jul 2025 — Dec 2025

    Software Engineer · Akcelita

    Designed and shipped an encryption service that let the internal platform handle sensitive data without re-architecting its APIs. Refactored 15+ endpoints around it and built an admin-only Workpages feature with role-based access.

    • .NET Core
    • React
    • Bouncy Castle
    • AWS KMS
    • Azure Key Vault
  5. Mar 2024 — Jun 2025

    Software Engineer · Puerto Rico Department of Health

    Maintained and extended Puerto Rico's public health surveillance platforms. Contributed to BioData (the public portal for infectious diseases) and to BioPortal, the platform health professionals use to report notifiable diseases.

    • Angular 19
    • .NET 9
    • Azure
    • SQL Server
  6. Jan 2023 — Mar 2024

    Back-End Engineer II · INVID

    Automated the daily generation of protection orders for Puerto Rico's judicial branch, so staff no longer had to come in on Saturdays to process them. Also shipped the end-to-end renewal and payment flow for a major car insurance provider.

    • C#
    • ASP.NET MVC
    • Entity Framework
    • Hangfire
    • Stripe
    • SSIS
  7. May 2021 — Dec 2022

    Software Engineer II · INVID

    Shipped features and platform improvements across three of the Puerto Rico judiciary's core systems: SUMAC (case management used by judges and court staff island-wide), RUA (the official attorney registry), and SIGNO (the notarial records system).

    • ASP.NET MVC
    • Razor Pages
    • CSLA.NET
    • Web Forms
  8. Jun 2018 — Apr 2019

    Software Engineer I · Wovenware

    Maintained and extended COPS, a SOAP-integrated sales tool for Claro PR's telecom offerings. Shipped features across Java web applications serving high-traffic customer portals.

    • Java
    • JSP
    • RichFaces
    • SOAP
  9. Mar 2018 — May 2018

    Mobile Developer (Internship) · Puerto Rico Innovation and Technology Service

    Contributed to accessibility improvements on Cesco Digital, the Puerto Rico government's consumer-facing mobile app, including code changes that enabled blind users to navigate the app with assistive technology.

    • React Native
    • Node.js

Education

  1. May 2026

    Master of Engineering, Computer Engineering

    Software Engineering Concentration · Polytechnic University of Puerto Rico

    Received a Design Project Expo Award for capstone work on unemployment and socioeconomic factors in Puerto Rico.

  2. 2019 — 2021

    PhD Coursework, Computer Engineering

    Polytechnic University of Puerto Rico

    • Completed 34 graduate credits as a recipient of the GAANN Fellowship (U.S. Department of Education).
    • Research focused on CIA security models for internet-connected FDA Class I medical devices in manufacturing environments.
    • Co-authored a peer-reviewed paper accepted to NSTA 2020, Computational Thinking Approach in K-12 Biology, with Dean Miriam Pabón and high school teacher Elena Bobonis. The conference was canceled due to COVID-19.
  3. May 2019

    B.S. Computer Science

    University of Puerto Rico at Bayamón

    Research Experience for Undergraduates (REU) at Columbus State University, summer 2017. Built a remote proctored-exam prototype with a Raspberry Pi, a webcam, and networking hardware.

Projects

  1. BioPortal & Bioresults

    Puerto Rico Department of Health

    Public health surveillance for Puerto Rico. Handles HL7 v2.5.1 lab-result ingestion from labs across the island and migrates legacy records into new investigation workflows.

    • .NET
    • Angular
    • HL7 v2.5.1
    • Azure
    • SQL Server
  2. BioData

    Puerto Rico Department of Health

    Public data portal for infectious diseases, health systems, and public health data in Puerto Rico. Open-access complement to BioPortal.

    • Angular
    • .NET
    • Azure
  3. RCI — Identity Provisioning

    Snac PR · PR Department of Justice

    Replaced a manual process where the DOJ subdirector fielded daily email requests for Active Directory access, validated them by hand, and activated accounts one by one. Automated intake from authorized agencies (PR Police, FBI, and others), with approval workflows, audit logging, and end-to-end account provisioning in AD and the application database.

    • .NET 10
    • Entity Framework Core
    • Angular 21
    • JWT
    • Active Directory
  4. Protection Orders Automation

    INVID · PR Judicial Branch

    Automated the daily generation of protection orders for Puerto Rico's judicial branch using SSIS and SQL Server. Eliminated weekend office visits for judicial staff.

    • SSIS
    • SQL Server
    • C#
  5. GenCyber-IoT

    Ladies Can Code Camp · GenCyber · Summer 2019

    A SQL injection demonstration tool built for the Ladies Can Code edition of GenCyber, a federally-funded summer camp focused on bringing young girls into cybersecurity. I designed and taught workshops on ethical hacking, network topology, programming with Ozobots, and IoT; this was the hands-on tool for the SQL injection workshop. Students typed a classic injection payload into a login form running against a Raspberry Pi and watched a database spill its contents.

    • Java
    • JavaFX
    • MySQL
    • Raspberry Pi