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VELRINO.

AI & FULL-STACK ENGINEER

Complex problems.
Thoughtful software.

I’m Denis. I turn complex workflows into products people can use. From AI for teachers to financial systems and games, I build across the whole stack.

Working globally

01 / SELECTED WORK

Ideas, shipped.

A few of the products I’ve helped bring to life. Explore the problem, the decisions, and what’s under the hood.

Architecture: Adapta Mídia01

COMPUTER VISION / AI

Adapta Mídia

Turn street activity into useful advertising insights.

  • Flutter
  • React
  • YOLO
  • Cloudflare
  • Cloud Run
  • Firebase
  • MongoDB
  • Redis
  • Vertex AI
  • Cloud Storage

Award-winning platform for outdoor advertising analysis and optimization using Computer Vision and Artificial Intelligence

An Android app built with Flutter runs YOLO (Ultralytics) for on-device computer vision, while the admin panel is a React web app deployed on Vercel. Both consume the same backend API.

Cloudflare sits in front of the platform as the edge layer — handling DNS, CDN caching, TLS, and protection — and routes every client request to the backend API.

The API runs on Google Cloud Run (serverless containers, auto-scaling). Firebase handles auth and realtime needs, MongoDB is the primary database, and Redis powers caching and the job queue.

Google Vertex AI provides the managed machine-learning layer for advertising analysis, and Google Cloud Storage holds media assets, uploads, and processed outputs.

What changed

Adapta Mídia received recognition at Adapta Summit and Adapta Hackathon in 2025 for applying AI and computer vision to outdoor advertising.

Adapta Mídia
Natiely02

GAMES / INDEPENDENT

Natiely

A world built from a lifelong love of games.

  • Unity
  • C#
  • Game development

My independent fantasy game, bringing together game development, art, music, and the experience of building a product from the ground up.

Architecture: ClassGame03

EDUCATION / 3D

ClassGame

A 3D classroom where AI helps students learn.

  • Next.js
  • React
  • TypeScript
  • Tailwind
  • Three.js
  • Go
  • Echo
  • Gemini
  • Vertex AI
  • Firestore
  • Redis
  • Cloud Tasks
  • Cloud Run
  • PostHog

ClassGame turns a teacher's lesson and worksheets into a short 3D review mission. Mia asks why a student chose a wrong answer, retrieves grounded lesson context, adapts the explanation, remembers how that student learns across sessions, and sends observable evidence back to the teacher in real time.

Next.js 16, React 19, TypeScript, Tailwind, and Three.js deliver two connected experiences. Students play adaptive missions in a mobile-friendly 3D classroom; teachers create, revise, publish, and monitor missions from a live evidence dashboard.

A Go and Echo API re-verifies Firebase identity, enforces class and mission authorization, pins every attempt to an immutable published revision, grounds question data server-side, and orchestrates synchronous tutoring plus asynchronous learning work.

Mission, Mia Tutor, and Learning agents call Gemini through Vertex AI with structured output. A policy and grounding gate combines retrieved lesson chunks, recent observable events, tutor history, persistent student memory, and class patterns before each model turn.

Firestore stores classes, versioned missions, exact attempt checkpoints, tutor turns, learning traces, long-lived student memory, and class synthesis. Redis enforces distributed quotas and health gates, while Cloud Storage keeps canonical published attachments.

Cloud Tasks delivers OIDC-authenticated jobs for attachment copies, learning-trace finalization, and the abandonment watchdog. Cloud Build and Artifact Registry deploy both services, while Cloud Logging and PostHog capture operational and product signals.

Browser Firestore access is read-only and role-scoped; students receive only safe projections. Leak guards protect teacher-only context, event IDs make tutor turns idempotent, quotas bound model spend, and every agent contract has a deterministic fallback.

Architecture: WPP AI04

MESSAGING / AI

WPP AI

AI conversations, inside WhatsApp.

  • Node.js
  • NestJS
  • React
  • Baileys
  • MongoDB
  • Redis
  • Bull
  • Gemini
  • OpenAI

Connecting WhatsApp with AI through a backend built around messaging, integrations, and reliable processing.

WhatsApp users and groups message the bot, while the React admin panel reads conversations, analyses, and authentication state through the same API.

Every message is resolved to a tenant, WhatsApp account, environment, and bot profile before persistence or AI work. That keeps customers, numbers, prompts, and histories isolated inside one deployment.

The NestJS API owns the Baileys adapter, auth, conversation, and orchestration modules. MongoDB stores tenants, accounts, conversations, messages, and analyses; Redis powers the Bull queue and operational cache.

Deterministic reviewers answer cheap simple cases without an LLM call. When a model is needed, the system wraps prompts with guardrails, uses Gemini as the primary provider, and falls back to OpenAI.

WhatsApp ingestion records the message and enqueues a job, keeping the socket responsive. A worker processes the analysis, validates output, completes or fails the audit snapshot, and sends the answer through the WhatsApp sender.

Architecture: GoatVPN05

PRIVACY / INFRASTRUCTURE

GoatVPN

A VPN with the infrastructure to back it up.

  • WireGuard
  • WGDashboard
  • NestJS
  • React
  • AWS
  • MongoDB
  • Redis
  • Stripe
  • Cryptomus
  • NoxPay

A NordVPN-style consumer VPN powered by WireGuard, with a fleet of servers managed through WGDashboard, a NestJS backend, a React app, and multi-gateway billing across Stripe, Cryptomus, and NoxPay.

An Android app and a React web client let users browse server locations and connect. Both authenticate against the same backend API and receive their WireGuard configuration from it.

The product runs on WireGuard, with a large fleet of servers orchestrated through WGDashboard. Capacity is provisioned across DataPacket and IS Hosting infrastructure for global, low-latency coverage.

A NestJS backend running on AWS exposes the API. MongoDB stores users, subscriptions, and server metadata, while Redis powers the job queue and caching layer.

Billing runs across multiple gateways — Stripe for cards, plus Cryptomus and NoxPay for crypto and alternative checkout — so users can subscribe through whichever method fits them.

ClickUp drives task management and Slack handles team messaging and system notifications. Subscription events are forwarded to Meta and Google tag managers to tag users and track conversions.

Cortex06

EDUCATION / AI

CoGrader / Cortex

AI feedback that reflects each teacher’s grading style

  • React
  • TypeScript
  • Node.js
  • Go
  • Redis
  • BullMQ
  • Vertex AI
  • Gemini
  • JEV
  • Firestore

I helped build Cortex, CoGrader’s new AI system, to adapt grading and feedback to each teacher as the product grew. My work spans handwritten document processing, reliable job queues, AI orchestration and the browser extension.

As CoGrader grew, one common AI approach could not reflect every teacher’s expectations. The challenge was to make feedback more personal while reliably processing the different files teachers upload.

Processed PDFs, scanned pages and handwritten student work with Go and Node.js. Redis-backed queues and idempotent processing let jobs retry without repeating their effects.

Orchestrated small agents with focused tasks and used JEV for classification, avoiding LLM calls for decisions that did not need them. Gemini 3.7 runs through Google Cloud Vertex AI, supported by credits received from Google.

Also contributed to the notification system, backend services and the React application, supporting the experience beyond the AI response.

What changed

Teachers loved the more personal results: the AI better reflected their grading style and expectations. Selective LLM use also reduced unnecessary AI calls.

CoGrader / Extension07

BROWSER EXTENSION / EDUCATION

CoGrader Extension

CoGrader, where teachers already work.

  • React
  • TypeScript
  • Plasmo
  • Tailwind
  • EdLink

Built the React and TypeScript browser extension from scratch, bringing CoGrader into Canvas, Blackboard, Schoology, Brightspace, Microsoft Teams for Education and Google Classroom. It increased interest in the main product and improved conversion by removing integration friction.

React and TypeScript power the interface, with Plasmo organizing the browser extension. LMS integrations bring grading into the tools teachers already use, helping them discover the main CoGrader product without changing their workflow.

Denis Velrino MagalhãesDENIS VELRINO MAGALHÃES

02 / THE PERSON BEHIND THE CODE

Curiosity started it. Building keeps it going.

I’m a self-taught software engineer working in technology since 2013. I’ve built banking systems, led engineering teams, and helped turn early ideas into working products.

Games taught me to explore, experiment, and keep trying. That same curiosity drives my work today, from AI products at CoGrader to my own game, Natiely.

Understand the problem. Build with care. Keep improving.

TOOLS, WITH A PURPOSE

From interface to infrastructure.

01

Product & interfaces

React · TypeScript · Next.js · Flutter · Unity

02

AI & processing

Node.js · Go · Gemini · Redis · AI agents

03

Systems & delivery

Google Cloud · AWS · Azure · Docker · Terraform

03 / THE JOURNEY

A career built by building.

Read my CV
2025 — PresentCoGraderFounding AI Full-Stack Engineer

I helped build Cortex, CoGrader’s new AI system, to adapt grading and feedback to each teacher as the product grew. My work spans handwritten document processing, reliable job queues, AI orchestration and the browser extension.

As CoGrader grew, one common AI approach could not reflect every teacher’s expectations. The challenge was to make feedback more personal while reliably processing the different files teachers upload.

Processed PDFs, scanned pages and handwritten student work with Go and Node.js. Redis-backed queues and idempotent processing let jobs retry without repeating their effects.

Orchestrated small agents with focused tasks and used JEV for classification, avoiding LLM calls for decisions that did not need them. Gemini 3.7 runs through Google Cloud Vertex AI, supported by credits received from Google.

Built the React and TypeScript browser extension from scratch, bringing CoGrader into Canvas, Blackboard, Schoology, Brightspace, Microsoft Teams for Education and Google Classroom. It increased interest in the main product and improved conversion by removing integration friction.

Also contributed to the notification system, backend services and the React application, supporting the experience beyond the AI response.

Teachers loved the more personal results: the AI better reflected their grading style and expectations. Selective LLM use also reduced unnecessary AI calls.

Backend & file processing

  • Go
  • Node.js
  • TypeScript
  • Express
  • Redis
  • BullMQ
  • Idempotent jobs
  • Firestore/Firebase Admin
  • Python
  • Zod

Frontend

  • React
  • Vite
  • Astro
  • Mantine
  • in-house design system
  • Tailwind
  • Plasmo
  • TypeScript

AI & integrations

  • Gemini 3.7 / Vertex AI
  • Small-agent orchestration
  • JEV classification
  • OpenAI
  • Anthropic/Claude
  • Google Classroom
  • Canvas
  • Blackboard
  • Schoology
  • Brightspace
  • Microsoft Teams for Education
  • EdLink
  • Stripe

Infrastructure & observability

  • Google Cloud
  • Azure
  • AWS
  • Terraform
  • Docker
  • Turborepo
  • pnpm
  • GitHub Actions
  • BigQuery
  • Dataform
  • Axiom
  • PostHog
Jun 2024 - Before CoGraderFintech & iGaming (NDA)CTO & Tech Lead

Led complete technical conception, development, and delivery of high-performance platforms in Fintech and iGaming before CoGrader.

Complete architecture of scalable platforms from scratch

Management of multidisciplinary technical teams (DevOps, Web Frontend, Mobile)

Implementation of recurring payment and cryptocurrency solutions

Integration with third-party APIs for security and compliance

  • NestJS
  • Node-ssh
  • Pusher
  • JWT
  • MongoDB Atlas
  • Redis
  • React
  • Next.js
  • Tailwind
  • AWS ECS
  • AWS Cognito
  • Docker
Mar 2023 - Jun 2024GO-K Digital (Grafeno Digital)Tech Lead & Senior Software Engineer

Led the Credit Emission project, transforming a complex manual process into an automated platform that reduced analysis time by 70% and expanded the company's operational capacity.

Architected scalable APIs with NestJS processing thousands of daily requests with 99.9% uptime

Implemented intelligent caching with Redis reducing query latency by 85%

Automated deploys with CI/CD eliminating 95% of human errors in production

Led team through structured IDPs, accelerating promotions and talent retention

  • NestJS
  • PostgreSQL
  • Redis
  • Docker
  • Kubernetes
  • React
  • TypeScript
  • Grafana
  • New Relic
Jul 2022 - Feb 2023Itaú BBATech Lead - Authentication & Permissions Squad

Led critical squad responsible for security and access control of millions of daily corporate transactions in the new Bankline, ensuring compliance and frictionless experience.

Architected corporate authentication solution with Auth0 supporting 50k+ simultaneous users

Achieved 90% test coverage (TDD) ensuring zero critical vulnerabilities in production

Implemented end-to-end encryption with Charon protecting billions in transactions

Delivered accessible system (WCAG 2.1) expanding user base by 15%

  • Java
  • Spring Boot
  • React
  • Auth0
  • AWS EKS
  • S3
  • CodePipeline
  • Voxel
Sep 2021 - Jul 2022TrustlyFIC Engineer

Solved the technical challenge of integrating payment gateway with American banks without public APIs, creating intelligent scraping solutions that process millions in monthly transactions.

Developed robust integrations with 15+ North American banks via resilient web scraping

Implemented multi-cloud rotation (AWS, GCP, Azure) maintaining 99.5% availability

Created change detection system preventing breaks before user impact

  • Java
  • PostgreSQL
  • Docker
  • Selenium
  • Scraping
  • Multi-Cloud
Jun 2019 - May 2021Itaú UnibancoSoftware Engineer - Mobile

Developed critical WebViews for Itaú mobile apps (Android/iOS) used by millions of customers, ensuring performance and consistent experience across multiple platforms.

Created reusable Angular components reducing development time by 40%

Optimized WebView performance improving load time by 60%

Automated deploys with AWS S3 + CodePipeline accelerating releases by 3x

  • Angular
  • TypeScript
  • AWS S3
  • CodePipeline
  • Java
  • Docker
  • Jenkins
Mar 2020 - Mar 2021SthormTechnology Consultant Senior

Full-stack consultant building ViralCure, a telemedicine platform that connected thousands of patients with healthcare professionals during the pandemic.

Developed complete platform from scratch reaching MVP in 3 months

Architected scalable solution supporting 10x traffic spikes

Implemented real-time scheduling system with multi-device synchronization

  • Angular
  • NestJS
  • PostgreSQL
  • Docker
  • Scrum
  • Trello
Apr 2018 - Jun 2019AccentureSoftware Engineer

Worked on Porto Seguro project developing highly complex corporate portals that optimized internal processes and improved experience for thousands of brokers.

Developed critical features in Angular with 99% end-user satisfaction

Integrated legacy systems with modern APIs reducing process time by 50%

  • Angular
  • Java
  • Spring
  • REST APIs
Apr 2016 - Jan 2017QueroQuitarSoftware Engineer

Developed critical integrations with multiple credit providers, automating debt negotiations and facilitating agreements that impacted thousands of people.

Integrated 20+ providers via REST and SOAP consolidating data from multiple sources

Implemented TDD ensuring 0 regressions in critical financial flows

Optimized MongoDB queries reducing response time by 70%

  • Angular
  • Laravel
  • Lumen
  • MongoDB
  • MySQL
  • Docker
  • TDD
Dec 2014 - Feb 2015IngresseSoftware Engineer Intern

Internship focused on backend development for ticketing platform, learning fundamentals of scalable APIs and high-performance architecture.

Developed REST APIs in PHP/Symfony processing thousands of daily transactions

Learned best practices for scalable architecture and production performance

  • PHP
  • Symfony
  • Nginx
  • REST APIs
Nov 2013 - Oct 2014Porto SeguroIntern

First professional internship where I learned software development fundamentals, teamwork, and agile methodologies in a corporate environment.

More work in banking & payments

Fintech Platform

Complete fintech platform supporting multiple payment methods, including cryptocurrencies

CTO & Tech Lead

Credit Emission System

B2B platform for corporate credit issuance and management

Tech Lead

Corporate Bankline

Development of Itaú BBA's new Bankline for corporate clients

Tech Lead - Authentication Squad

Payment Gateway Integration

Payment gateway integration with North American banks

FIC Engineer

04 / BEYOND THE DAY JOB

Build. Share. Repeat.

1ST PLACE · ADAPTA SUMMIT 2025

An idea that earned its place.

Adapta Mídia received recognition at Adapta Summit and Adapta Hackathon in 2025 for applying AI and computer vision to outdoor advertising.

Adapta Mídia

COMMUNITY / OPEN SOURCE

Knowledge travels further when shared.

Talks and workshops on software, AI, and the practical decisions behind real products.

View the WhatsApp + AI talk

COMMUNITY / OPEN SOURCE

Learning means more when we share it.

I love sharing what I learn. I organized meetups and hands-on workshops to help beginners take their first steps in development, ask questions, and build together.

Frontend & Backend Workshop - Beetech

Frontend & Backend Workshop - Beetech

In-person workshop teaching full-stack development to the tech community at Beetech (https://beetech.global/)

Git & Version Control Workshop - SENAI

Git & Version Control Workshop - SENAI

Training on version control and best practices with Git at SENAI

Mobile Development Workshop - Itaú

Mobile Development Workshop - Itaú

Internal event at Itaú focused on mobile development and networking among developers

Flutter + AdonisJS - FATEC Zona Sul

Flutter + AdonisJS - FATEC Zona Sul

Presentation on Flutter integrated with AdonisJS, market trends, and emerging technologies for students (03/04/2025)

05 / LET’S TALK

What are you building next?

Have a product challenge or an engineering role in mind? Tell me what you’re working on.

Start a conversation