Michal Lacko, Developer in Bratislava, Bratislava Region, Slovakia
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Michal Lacko

Verified Expert  in Engineering

Back-end Developer

Bratislava, Bratislava Region, Slovakia
Toptal Member Since
July 30, 2021

Michal is a back-end-first Scala developer with 6+ years of experience creating robust solutions that scale on demand. He has experience building projects from the ground up, from defining the database schema and architecture to web development. He enjoys functional programming over OOP whenever it makes sense. Michal has also proven to be a team player with the end goals in mind.


Scala, ZIO, ZIO HTTP, Caliban, MongoDB
Upstart Commerce
Scala, ZIO, Doobie, Quill, PostgreSQL, Http4s, Akka, Circe, Caliban, Back-end...
Scala, Framework7, Scala.js, React, Http4s, ZIO, Doobie, PostgreSQL, Slinky...




Preferred Environment

Slack, Zoom, IntelliJ IDEA, Terminal, MacOS

The most amazing...

...side-project I've created—Ideas Filter—was #1 on hacker news for a while, which was really surprising and motivating.

Work Experience

Senior Scala Developer

2021 - PRESENT
  • Developed a project which consumed a Kafka topic with an email request. The project included throttling with feature flag settings and rotating usage of email providers.
  • Developed a project with REST API and GraphQL to process incoming requests to notify data subjects at a large scale. Working on the project also included integration with external and internal services via rest/GraphQL.
  • Updated older codebases for the newest library versions allowed us to integrate with projects that were already using the latest versions. Introduced zio-HTTP to the company tech stack.
Technologies: Scala, ZIO, ZIO HTTP, Caliban, MongoDB

Scala Developer

2020 - 2021
Upstart Commerce
  • Build a REST and GraphQL service used as a CRUD application for ratings and reviews of shop items—one of my most significant projects.
  • Handled customer feature requests and bug reports.
  • Migrated the project libraries to the latest possible versions.
  • Worked on the integration project connecting the ratings and reviews platform with other projects. This project included listening to Kafka events, propagating changes, and integrating them with the authorization service.
Technologies: Scala, ZIO, Doobie, Quill, PostgreSQL, Http4s, Akka, Circe, Caliban, Back-end, SQL

Full-stack Scala Developer

2020 - 2020
  • Generated the Scala wrap and facets code from the original Framework7 TypeScript code.
  • Built the web front end using Scala.js, Framework7, and Slinky with a mobile-first approach in mind, including PWA requirements.
  • Designed the PostgreSQL schema that was supposed to keep consistent user social network data.
Technologies: Scala, Framework7, Scala.js, React, Http4s, ZIO, Doobie, PostgreSQL, Slinky, Full-stack, Back-end, Front-end, SQL

Scala Developer

2019 - 2020
Chili Piper
  • Designed and built a multitenant email inbox application presented at the Dreamforce conference, a global family reunion for stakeholders. The inbox did synchronize with Gmail email data.
  • Supported all Gmail functionality within the app, with additional features such as smart search across your colleague's inboxes, live discussion and commenting on emails, real-time push notifications via WebSockets, and Salesforce integration.
  • Reduced tech debt and bug fixes, working part-time on an already existing legacy revenue-generating codebase.
Technologies: Scala, ZIO, PostgreSQL, MongoDB, API Integration, Back-end, SQL

Scala Full-stack Developer

2018 - 2019
  • Implemented a customizable reporting page that included integration with JasperReports Library, a Jaspersoft product that allows report generation and rendering, and D3.js on a large Scala multi-project used by many pig farms.
  • Introduced Monix to the team, which improved our codebase in terms of dealing with concurrency and parallelism.
  • Contributed to the project's deployment to production.
Technologies: Scala, Play, Scala.js, React, Monix, PostgreSQL, Full-stack, Back-end, Front-end, SQL

Senior Scala Developer

2017 - 2018
  • Implemented a REST API and was tasked to create a library with an Akka stream and source to consume Kafka messages. The library I built also handled special cases, including error handling and concurrency.
  • Implemented an algorithm for seating groups on tables so that the number of groups split on multiple tables was minimal. For this, I used my knowledge of computer science, namely on the Least Cost Branch and Bound algorithm.
  • Joined the US team and contributed to the deployment of specific versions to production.
Technologies: Scala, Apache Kafka, Slick, Play, Oracle, Back-end, SQL

Scala Architect Developer

2015 - 2017
Spring Business Accelerator
  • Implemented the messaging system that allowed end-users to store, send, and retrieve messages from various independent platforms and email as part of a two-person team.
  • Integrated with the Auckland Transport REST API and built a middle layer later used by the mobile clients. The middle layer acted as a nonpersistent data storage with some data tuning.
  • Created a user data collection tool that made series of inquiries that the end-user could answer.
  • Added a Scala.js subproject to the existing multi-project. The module allowed us to share type-safe structures between the back end and the front end and store the code under one repository.
Technologies: Scala, Play, Akka, Erlang, Ejabberd, Scala.js, API Integration, Back-end


A Google Trends' alternative that I created with Reddit user content data. The project periodically reads every new Reddit post and stores statistics about each keyword.

This is a side-project that I implemented in my free time. I used Scala, ZIO, Doobie, PostGREST, Http4s, Circe, Scala.js, Slinky, and React.

Ideas Filter

A simple list of apps and other solutions that exist on a few popular marketplaces. The idea is to find apps that could be cloned and made better.

I ensured that the data was gathered periodically via web crawling for this side-project, and I also learned and integrated with Firebase.

Ideas Filter was number one on hacker news for a while. More information about this project is available on https://news.ycombinator.com/item?id=27007767.

Algo Strategies

A simple side project created in pure Scala.js. The project accepts your CSV financial market time-series data and runs some strategy discovery genetic algorithms. The process distributes the work via web workers to make use of several CPU cores in parallel. The web workers and the communication between them were also implemented in Scala. I implemented this side project in my free time alone. The website stores the users' data in local storage; there's no back end or database.


An eCommerce market intelligence tool that crawls the web to aggregate millions of products—namely name, price, image, category, and description—and offers valuable analytics regarding competition awareness and product trends to users.

I worked on this tool as the sole full-stack developer, creating an ML algorithm to detect which pages contain a product description. The project was build using Scala, PostgreSQL, Scala.js, and Akka.


A background job that posts predefined comments (defined by the customer) on Reddit whenever a new post that contains some keywords is detected.

This side-project of mine was made with 100% Scala, including the back and front end with Scala.js and Laminar.

Crypto Coin Screener

A crypto coin screener web solution. Gathering data from various places like coin gecko API and coin scan website scraping. Coin data is stored in PostgreSQL DB. Data gathering and REST API back end are both built with ZIO. The front end is built with Scala.js and Laminar. The web allows filtering for crypto coins based on desired properties, like price, volume, ownership, and their changes.
2009 - 2014

Master's Degree in Computer Science

Comenius University - Bratislava, Slovakia


The Data Scientist’s Toolbox



R Programming



Scala.js, ZIO, Doobie, Http4s, Circe, Caliban, React, Web Worker, Monix, Slick, Reddit API, REST APIs, ZIO HTTP




Scala, Erlang, SQL


Functional Programming


Akka, Framework7, Play, Tailwind CSS


PostgreSQL, MongoDB


Firebase, MacOS, Apache Kafka, Oracle


Web Scraping, APIs, Machine Learning, Artificial Intelligence (AI), Slinky, Ejabberd, Full-stack, API Integration, Back-end, Front-end, Cloud Security

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