Lazar Kocic Email me
Valencia, Spain

Lazar Kocic

Senior & lead software engineer

I build web products end to end, with React and TypeScript at the front and Node at the back. Twelve years of it, from a national energy market to smart TVs to streaming for government institutions.

lazar.kocic1990@gmail.com

See what I've built Email me
Building right now

Parlor Table

What I am building right now. Around thirty classic card, dice and domino games on a real table, from Klondike and Hearts to Cribbage and Train Dominoes, with 3D dice and computer opponents at three levels. Play straight away with no account, and a daily deal for every game.

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My own products

Things I've built and run myself

Each one designed, built, deployed and looked after by me, end to end. Open any of them.

  • Parlor Table

    In progress

    What I am building right now. Around thirty classic card, dice and domino games on a real table, from Klondike and Hearts to Cribbage and Train Dominoes, with 3D dice and computer opponents at three levels. Play straight away with no account, and a daily deal for every game.

    • Hono
    • Three.js
    • Workers
    • D1
    • R2

  • LingoStories

    lingostories.app ↗

    Learn a language by reading. Graded stories, grammar lessons and everyday phrases, across 12 interface languages.

    • Next.js
    • Workers
    • D1
    • R2

  • Rambleo

    rambleo.com ↗

    A language game you walk through. Wander a 3D city, step into the buildings and hold a conversation with whoever is inside.

    • React Three Fiber
    • Rapier
    • Workers
    • D1

  • Mathorio

    mathorio.com ↗

    Free interactive maths platform with 300+ lessons, step-by-step solutions, interactive graphs and real-world examples, in six languages. No paywall, no ads.

    • Next.js
    • Workers
    • D1

  • Quizotle

    quizotle.com ↗

    A quiz game with a server-driven engine, covering quizzes, arcade, duels, tournaments and leagues. Coins are an append-only ledger, so scoring and spending can never race each other.

    • React
    • Hono
    • Workers
    • D1
    • R2

  • Tipelly

    tipelly.com ↗

    A free social game of predicting football, basketball and tennis results, with private leagues, localised for the Balkans. Signing in is a magic link and nothing else, with no passwords and no OAuth.

    • React
    • Hono
    • Workers
    • D1
    • KV

  • World Stroll

    worldstroll.com ↗

    Learn the whole world, one short stroll a day. A country of the day with its map, flag, food, phrases and a quiz, geography categories and daily games, and a passport stamp for every country you finish. Free, written for adults.

    • Hono
    • Workers
    • D1
    • R2
    • Cron

  • Daily Ancestor

    dailyancestor.com ↗

    Teaches family historians to read the records their ancestors left behind. A dictionary of old record words, a record of the day on a real scan, detective cases, and tools like birth year from a census or a headstone and Soundex. Free, no account needed.

    • Hono
    • Workers
    • D1
    • R2

  • Own Your Guests

    ownyourguests.com ↗

    Direct-booking websites for holiday rentals on the US and UK markets. Every client's public site, admin panel, photos and calendar are served by a single Worker. Colours, copy and sections are data rather than code, and the money lands in the owner's own Stripe account.

    • Hono
    • Workers
    • D1
    • KV
    • R2
    • Stripe Connect

  • Own Your Tours

    ownyourtours.com ↗

    The same platform pointed at tour and activity operators: boat trips, diving, wine tours, cooking classes. The unit of booking is a time slot with capacity instead of a range of nights, and the price follows the type of participant.

    • Hono
    • Workers
    • D1
    • KV
    • R2
    • Stripe Connect

  • Second Brake

    secondbrake.com ↗

    Booking sites for driving schools with a handful of instructors. One booking holds an instructor and a car at the same time, which is the thing generic scheduling software gets wrong, and lesson packages are a ledger in minutes rather than a counter.

    • Hono
    • React
    • Workers
    • D1
    • KV
    • R2
    • Cron

  • Steady Class

    steadyclass.com ↗

    Enrolment and monthly tuition for kids' activity schools in the US: martial arts, dance, music, gymnastics. A family is one payer with one card, and belt or grade names are data rather than code, so one product covers six disciplines. Parents get in through a passwordless link.

    • Hono
    • React
    • Workers
    • D1
    • KV
    • R2
    • Cron
Selected work

Products I built for companies and institutions

Products I helped build for companies and institutions. Roughly in reverse order, though the order matters less than the problems.

  • Babscast

    iBabs

    Enterprise streaming platform used by government institutions across the Netherlands. A custom Video.js player with live overlays for speakers, topics, slides and notifications, plus a backstage timeline tool that drives the whole broadcast. Microservices behind a BFF, LiveKit for the stream.

    • React
    • TypeScript
    • Video.js
    • LiveKit
    • Microservices
    • BFF

  • Rivet

    Company Webcast

    Webcast and webinar platform for a Euronext company. Three connected portals (company, client and management) on one shared component library, plus a custom player and a backstage app, over a microservices and BFF backend.

    • React
    • TypeScript
    • Microservices
    • BFF

  • E-Mitwirkung

    Konova AG

    Switzerland's most widely used e-participation platform, with 140+ municipalities, cities and cantons running their public consultations on it. Laravel on the back, React on the front, and a Storybook component library that lets every customer restyle the whole thing.

    • React
    • TypeScript
    • Laravel
    • Storybook

  • Ais Play

    Sky Soft / Syrmia

    A Netflix-style Smart TV app for Samsung Tizen and LG webOS, with live channels, video on demand, EPG, remote-control focus navigation, favourites, kids and lock modes. Led a team of 15+ engineers from start to release.

    • React
    • Node.js
    • Samsung Tizen
    • LG webOS

  • One Suite

    Logistics ERP

    End-to-end ERP for a logistics company. API and web app covering vendors, distributors and customers, booking flows, inbound and outbound operations, down to HR and leave management.

    • React
    • TypeScript
    • Node.js
    • MySQL

  • Device Management

    Sky Soft / LMB

    Monitoring platform for medical devices in the field: devices report their state, the system tracks alerts and messages in real time and surfaces them on a React dashboard.

    • Node.js
    • React
    • Real-time

  • MTS

    Australian energy market

    The transaction system at the centre of Australia's national electricity market, built by ten distributed teams. Backend work in .NET with Oracle stored procedures, on a high-volume, mission-critical platform.

    • .NET
    • C#
    • Oracle

  • Home Stats

    Sky Soft

    Consumption analytics front end for utility customers in Slovenia — water, gas and electricity. Interactive charts, comparative statistics and large data tables, tuned to stay responsive on big time-series datasets.

    • React
    • JavaScript
    • Data visualisation
    • Charts & dashboards

  • Algreen Retail

    Algreen

    Retail web application for a door manufacturer, built around an interactive door configurator. Customers assemble a door — single or double, glass, peepholes, handles, every part — with the result rendered live as materials and options change, and an automatically generated quote at the end. Complex rule-based configuration logic and pricing on a Laravel backend, Vue on the front.

    • Laravel / PHP
    • Vue.js
    • JavaScript
    • MySQL

  • MAP

    Post of Serbia

    Large web system used by Post of Serbia staff across the network, covering money transfers (RIA, MoneyGram), shipments and courier management.

    • .NET
    • jQuery
What I do

What I work with

Bigger type means more of my time goes there. The small ones are things I have shipped with when a project asked for them.

  • Product frontends

    React and TypeScript, design systems, and Storybook component libraries that teams actually reuse.

  • Backends & integrations

    Node.js services, REST API design, BFF layers in front of microservices. Laravel and .NET when the stack calls for it.

  • Real-time & video

    Custom players, live overlays and streaming pipelines, built on Video.js, LiveKit and SignalR.

  • Web performance

    Core Web Vitals, bundle and render profiling, caching strategy, SSR and SSG.

  • Leading delivery

    Teams of up to 15+ engineers, and the pipelines behind them: GitHub Actions, GitLab CI, Bitbucket.

  • Shipping on Cloudflare

    Workers, D1 and R2: whole products running on the edge, database and file storage included.

  • Frontend

    • React
    • TypeScript
    • JavaScript
    • Next.js
    • Storybook
    • Design systems
    • CSS, accessibility
    • React Three Fiber
    • Tizen, webOS

  • Backend and APIs

    • Node.js
    • REST APIs
    • BFF, microservices
    • Hono
    • PHP, Laravel
    • .NET, C#

  • Testing

    • Unit tests
    • Vitest
    • Playwright
    • Testing Library

  • Cloud and delivery

    • Cloudflare Workers
    • GitHub Actions
    • GitLab CI
    • AWS
    • Bitbucket Pipelines

  • Data

    • MySQL
    • SQLite, D1
    • KV, R2
    • Oracle

  • Real-time and video

    • Video.js
    • WebSockets
    • LiveKit
    • SignalR
A bit more

About me

I'm from Niš, and these days I live in Valencia. I studied electronic engineering back home and finished my master's with a 9.70, then spent the next twelve years finding out how little of it you use and how much of it you need.

Most evenings still end with something new shipped, usually a little before it was ready.

Need a website for your business?

New websites with a panel you edit yourself, free website checks, and ready booking systems for five trades.

For business Website pricing