Matheus Castro

WhoAmI

Hey, I'm Calvo, Matheus's AI sidekick. Start here: who he is, what he loves and the stack he builds with.

MatheusCastro --background

Active TS/SCI clearance

I'm Matheus, a software engineer from Brazil who moved to the United States as a young adult, learned the language and the culture from scratch, and has been adapting quickly ever since. I come from the U.S. Army, where I supported mission-critical air defense systems. I hold an active TS/SCI clearance, and I'm an alumnus of Microsoft's Software and Systems Academy (Cloud Application Development), where I built web and desktop applications. I've loved technology for over six years, I'm married, and I'm looking for a team of experienced engineers to grow with.

hobbies.yaml

hobbies:  - Gaming  - Guitar  - Gym  - Hiking  - Cooking  - Making wife happy

outside of being a dev

hobbies.svg

techStack.json

{  "Languages": ["C#", "XAML", "JavaScript", "TypeScript", "SQL", "Python", "Markdown"],  "Frontend": ["React", "Next.js", "Tailwind CSS", "shadcn/ui", "Base UI", "Vite"],  "Backend": [".NET", "ASP.NET", "Node.js", "Express.js", "Dependency Injection"],  "Desktop": ["WPF", "Windows Forms", "MVVM", ".NET MAUI"],  "Data": ["MongoDB", "PostgreSQL", "SQLite", "Entity Framework Core", "Redis", "SQL Server"],  "Cloud & DevOps": ["Vercel", "Azure", "GitHub Actions", "CI/CD", "CodeQL", "Dependabot", "GitHub Advanced Security", "Turnstile", "Resend"],  "AI": ["Claude", "Claude Code", "GitHub Copilot", "Vercel AI SDK", "Anthropic C# SDK"],  "Testing & Quality": ["xUnit", "Vitest", "Build Validation", "Claude Code Review", "node:test"],  "Practices": ["Agile"]}

projects/

Harnesses

Just hanging around. Matheus built these harnesses to keep AI coding agents consistent, reliable and cheap.

AI work made consistent and reliable

What it is

HarnessEngineering101 is study material on configuring an AI coding agent's context, rules, subagents and skills, with examples from BabyBuddyHelper and InvoiceMe. ProdHarnessConfig is the production Claude Code harness that grew out of it: it takes a GitHub issue from plan to merge, with a person deciding at two gates.

What it solves

Makes AI-assisted development repeatable and cheaper, measured on every issue, without giving up human review.

Tech stack

  • Claude Code (skills, subagents, hooks)
  • Claude (Opus and Sonnet)
  • Node.js / JavaScript
  • Markdown

Tooling

  • node:test suites
  • GitHub Actions and rulesets
  • Metrics collection and meta-analysis per batch of runs through Claude Code

Links

InvoiceMe

Yes, I'm standing on an invoice. Don't worry, InvoiceMe keeps a copy. Customers and invoices for small businesses, in one place.

A Customer and Invoice management solution for small business

What it is

A full-stack business management app that lets small-business owners keep customer records and create and look up invoices.

What it solves

Gives small businesses a lightweight, single place for customers and invoices, with tax calculated by state.

Tech stack

  • MongoDB
  • Express.js
  • React (Vite)
  • Node.js
  • Tailwind CSS

Tooling

  • CodeQL
  • Node.js CI (Build Validation)
  • Dependabot Dependencies Update
  • GitHub Advanced Security (for secrets and keys)

Links

BabyBuddyHelper

Bottle in my pocket, pacifier in hand: BabyBuddyHelper takes some of the load off new parents.

A guardian angel for tasks and vaccination tracking

What it is

A cross-platform parenting companion built with .NET MAUI for tasks, appointments, baby profiles and vaccine tracking. Cub, an animated companion, answers everyday baby-care questions through Claude.

What it solves

Helps caregivers keep track of routines and baby-care tasks in one low-stress place.

Tech stack

  • .NET MAUI
  • C# / XAML
  • SQLite via EF Core
  • Anthropic C# SDK (Cub, powered by Claude)
  • Dependency Injection for internal and external services

Tooling

  • CI/CD through GitHub Actions
  • Build Validation
  • xUnit Test Validation
  • CodeQL
  • Claude Code Review
  • Dependabot Dependencies update

Links

Other Work

  • MyStudyTime

    Helps students organize their notes, use flashcards and plan their study schedule. WPF, .NET 8, C#, MVVM, Entity Framework 6 with SQL Server.

    Repository for MyStudyTime

  • StudentRegistry

    Manages student records, with teacher authentication, GPA tracking and automatic awards for top performers. .NET 10, Windows Forms.

    Repository for StudentRegistry

  • MSSA Work

    Cloud Application Development projects and assignments from the Microsoft Software & Systems Academy. C#.

    • 86 projects
    • 18 weeks
    • 8 certifications
    • 317 hours
    Repository for MSSA Work

  • Obsidian Knowledge Vault

    A software engineering "second brain" in Obsidian, with notes and references on most major software engineering topics.

    • 81 notes
    • 15 sections
    Repository for Obsidian Knowledge Vault

Thanks for scrolling this far. That's everything, for now.

Back to top