jonathas.net

Software Crafter · Porto, Portugal

Hello, World! I’m Jonathas.

A passionate software engineer who loves transforming ideas into reality. Dive in to explore my journey, projects, and the cool stuff I’m working on.

See my work Get in touch
Diagram: on Azure, clients call an API gateway and a .NET API that stores data in SQL Server, Cosmos DB and Blob Storage, works with AI agents and hands slow work to Service Bus queues. AWS Lambda processes those events and calls external integrations. GitHub Actions deploys the API and Grafana monitors it. AZURE AWS DEPLOY METRICS ASYNC EVENTS APIS GitHub Actionsci · cd Grafanadashboards Clientsweb · mobile API Gatewayrest · https .NET APIasp.net core SQL Serverrelational Cosmos DBdocuments Blob Storagefiles AI agentsllm · tools Service Busqueues · async Integrationserp · partner apis AWS Lambdaevents · batch AZURE Clientsweb · mobile Gatewayhttps .NET APIasp.net core SQLserver Cosmosdb Blobstorage AI agentsllm · tools Service Busqueues

01Portfolio

Featured projects

Screenshot of json2types: the JSON to C# page with a sample order on the left and the C# classes generated for it on the right

json2types (opens in a new tab)

Paste JSON, get C# classes or records and TypeScript interfaces as you type. It merges every sample to find what’s optional and nullable, sizes numbers exactly, and runs entirely in the browser.

  • TypeScript
  • Vite
  • Web app
json2types.jonathas.net
Screenshot of the Original Table Games lobby: Entre Dados, Alvo Móvel and Espelho open to play, Trancar in development, and a balance in virtual chips

Original Table Games (opens in a new tab)

Four original casino table games: the player rolls the dice and the dealer deals the cards. Three are ready to play with virtual chips, their math proven exactly and by simulation.

  • In development
  • TypeScript
  • PixiJS
jonathascosta.github.io
Screenshot of the Salary Converter: 3,000 euros a month converted to BRL, USD and GBP per hour, day, week, month and year

Salary Converter (opens in a new tab)

Converts a salary between hourly, daily, weekly, monthly and yearly pay in BRL, USD, EUR and GBP, with the Central Bank of Brazil’s exchange rates and shareable links.

  • TypeScript
  • Vite
  • Web app
salary-converter.jonathas.net

02Games

Games to play

Screenshot of Arrows: level 1, a board of arrow-shaped paths pointing up, down, left and right

Arrows (opens in a new tab)

A calm, clever puzzle: tap the arrows out, one by one, and clear the board. Endless levels, a daily challenge and a league, now on the App Store and on the web.

  • TypeScript
  • Capacitor
  • iOS
arrows.jonathas.net
Screenshot of Decanta: level 40, super hard, with eleven glass tubes of layered colors and two empty tubes

Decanta (opens in a new tab)

A calm water sort puzzle: pour the colors until every tube holds one. Endless levels, a daily puzzle and a league, on the web now and soon on the iPhone.

  • TypeScript
  • Capacitor
  • iOS
decanta.jonathas.net
Screenshot of Moat: level 40, super hard, an empty 8 by 8 board split into eight colored realms

Moat (opens in a new tab)

A calm castle logic puzzle: one castle per row, column and realm, none touching. Endless levels, a daily challenge and a league, on the web now and soon on the iPhone.

  • TypeScript
  • Capacitor
  • iOS
moat.jonathas.net
Screenshot of Drift in play: neon enemy ships in pink, violet and yellow fill the screen as the player’s ship fires from the bottom

Drift (opens in a new tab)

A neon arcade space shooter for one thumb: waves of enemies, bosses and power-ups worth the risk. Endless runs and a daily run, on the web now and soon on the iPhone.

  • TypeScript
  • Capacitor
  • iOS
drift.jonathas.net
Screenshot of the Sudoku: a medium puzzle in progress, with the player’s digits in blue, pencil-mark notes, a selected cell and the number pad

Sudoku (opens in a new tab)

A Sudoku with three levels, notes, undo and hints. It saves your game as you play and works offline.

  • TypeScript
  • Vite
  • PWA
sudoku.jonathas.net

03Articles

Latest posts

RSS feed

  1. 7 min read

    Inferring C# and TypeScript Types from a JSON Sample

    How json2types turns pasted JSON into C# classes and TypeScript interfaces: keeping the text of every number, merging every sample instead of reading the first, sizing integers and decimals exactly, typing dates only when every value is one, choosing names every compiler accepts, and testing the output against the real .NET and TypeScript compilers.

  2. 6 min read

    Polly v8 in Practice: Retries, Circuit Breakers and Timeouts That Behave

    Polly v8 replaced policies with resilience pipelines, and Microsoft.Extensions.Http.Resilience made a sensible default one line. What each strategy actually does, measured against a deliberately flaky local server: jittered backoff, a breaker that fails in a hundredth of a millisecond, timeouts that cancel the request, and why the order of strategies matters.

  3. 5 min read

    Testcontainers in .NET: Integration Tests Against the Real Database

    EF Core's in-memory provider passes tests that the real database fails: unique indexes, column lengths, foreign keys and decimal precision are all ignored. Testcontainers starts a real PostgreSQL per test run in about three seconds. The same four tests, both ways, with real timings and a setup that keeps a hundred tests under a second.

  4. 7 min read

    AI Agents in .NET: Tools, a Loop and the Guardrails That Matter

    An agent is a model, a set of tools and a loop. With Microsoft.Extensions.AI that's a few dozen lines of C#. The work is in the guardrails: rules enforced in code, approvals for actions that change things, a cap on the loop, and tests that don't need a model. A support agent built and run against a local model, with its real output.

All 19 articles

04Journey

Latest on my journey

Show my journey as

  1. 2025 – present

    Ardanis / Plain Concepts, Senior Software Engineer

    • Insurance
    • Financial analytics
    • Mining

    Three clients so far: .NET, SQL Server and Azure for PremFina; Aileen, Ardanis’s AI contact-center platform, for SOBI Analytics; and an AI agent that answers questions about Anglo American’s haul trucks and mining equipment.

    • .NET
    • SQL Server
    • Azure
    • AI agents

  2. 2024 – 2025

    Proxify / Univet, Senior Software Engineer

    • Veterinary pharmaceuticals

    For a veterinary-pharmaceutical client, I automated batch creation and deployment, migrated the legacy app to .NET 8, and developed a proactive monitoring system.

    • .NET 8
    • Automation
    • Monitoring

  3. 2024

    YLD / NewDay, Senior Software Engineer

    • Credit cards & payments

    I worked at NewDay through YLD, on a team responsible for payments, utilizing .NET Core, Cosmos, and REST APIs.

    • .NET Core
    • Cosmos DB
    • REST APIs

  4. 2023 – 2024

    22 cans, Senior Software Engineer

    • Gaming

    Transformed software pipelines with GitHub Actions, authored open-source libraries, overhauled server architecture with AWS Lambda, and built monitoring tools using ASP.NET and ECMAScript 6.

    • GitHub Actions
    • AWS Lambda
    • ASP.NET
    • ECMAScript 6

  5. 2022

    Ascent, Technical Architect

    • Scientific research

    Strengthened SQL Server infrastructure, contributed to a global pharma research app, and conducted code reviews.

    • SQL Server
    • Code review

  6. 2020 – 2022

    KCSIT / Mindera, Senior Software Engineer

    • Insurance
    • Transportation
    • Credit cards & payments

    Built a new API for claims ticket management in the insurance industry using SQL, REST, and ASP.NET Core; contributed to a hybrid ticket type in transportation, integrated systems for customer credit and address validations, improved system resilience to 99.99%, implemented a high-speed batch process for 1 million customers, and developed a Grafana dashboard for real-time API monitoring.

    • ASP.NET Core
    • SQL
    • REST
    • Grafana

  7. 2017 – 2019

    Farfetch, Lead Engineer

    • Luxury fashion

    Performed as a lead developer for the high-traffic product display page, overseeing 10,000+ requests per minute, conducted monthly one-on-one meetings with a team of ten engineers and QA professionals, balanced team backlog with the product owner, and managed feature releases and A/B testing.

    • Leadership
    • High traffic
    • A/B testing

05Contact

Let’s build something amazing together.

The best way to reach me is on LinkedIn.

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