English version. Leia esta página em português.
Who I am
I am a senior backend engineer with nine years on the JVM. Kotlin is my primary language, and most of my career has been in fintech: card payments, credit-bureau data and lending. I work remotely from São Paulo, Brazil, and I have delivered to teams in the United States, Canada and France, in English, for five years.
Open source
I am a core maintainer of Kotest, the leading Kotlin testing framework, with 4.8k stars on GitHub and production use worldwide. I own its assertions module, the part most Kotlin engineers touch every time they write a test: public API design, deprecation cycles, binary compatibility enforced in CI, and multiplatform releases. Those decisions are made in public, asynchronously, by consensus with the other maintainers, and a bad one cannot be quietly rolled back once the ecosystem has it.
I also contributed to Koin, the Kotlin dependency-injection framework, while at Kotzilla, the company behind it. Alongside that I have published Kotlin/JVM libraries (Brazilian document validation, password generation, Kotlin extensions) and five Android apps on Google Play.
Writing and speaking
I have written 60+ published technical articles on Kotlin, Java and the JVM for Baeldung, one of the largest JVM publications, since 2022. It is paid, edited work, not a hobby blog. I have also been a guest speaker at the University of São Paulo on software testability, mutation testing and clean code.
Experience
- Colman Software (2021–present) — my own consultancy. Contract backend engineering for e-commerce and mobile clients: Kotlin/Java, PostgreSQL, AWS, REST APIs, CI/CD. I design the architecture, run it in production, and I am the one paged when it breaks.
- Clutch (2024–2025) — fintech for credit unions, on a TypeScript codebase. Owned the vehicle-credit lending endpoint end to end, and replaced manual QA with automated coverage on flows that had none.
- Kotzilla (2023–2024) — the company behind Koin. Contributed to the framework and built Cloud-Inject, its profiling platform.
- Triton Digital (2021–2023) — digital audio infrastructure. Built partner-facing ad-campaign features used by broadcasters across North America, and introduced CI/CD where there was none.
- Guiabolso (2019–2021) — Brazil’s largest personal-finance app at the time. Senior engineer, and the technical lead on real-time alerts that told a user the moment a debt appeared on their credit-bureau file, built for its full base of 12M+ users. Promoted to senior within six months.
- PagSeguro (2017–2019) — one of Brazil’s largest card payment processors. Introduced Apache Kafka to a team with no streaming infrastructure: took a nightly batch job out of a monolith and rebuilt it as an event-driven pipeline over 2M+ customers.
What I work with
- Languages: Kotlin (expert), Java (expert), Scala, TypeScript, SQL
- Backend: Spring Boot, Ktor, Koin, REST APIs, microservices, monolith decomposition
- Distributed systems: Apache Kafka (self-managed and Confluent), event-driven architecture, message ordering, idempotency, reprocessing without duplication, Apache Spark
- Data: PostgreSQL, MySQL, DynamoDB
- Infrastructure: AWS, Docker, Kubernetes, CI/CD, GitHub Actions, Datadog
- Testing: Kotest, JUnit, MockK, TDD, BDD (Cucumber), mutation testing
- AI in the development lifecycle: I build with Claude Code daily, and I have been paid to review code used to train and evaluate large language models
Education
- MSc, Computer Science / Artificial Intelligence — University of São Paulo (2021–2022). Coursework completed; thesis not defended. Research on classification of unstructured text data.
- BSc, Information Systems — University of São Paulo (2016–2020).
Languages
Portuguese (native), English (fluent, Cambridge C1), Spanish and French (intermediate).
Get in touch
leonardo@colman.com.br · LinkedIn · GitHub