Biography & Overview

Cezar Sampaio

Lead Frontend Engineer @ On • Berlin, Germany

I am a Lead Software Engineer with 15 years of experience building web platforms at On, HelloFresh, Contentful, and Trade Republic. I combine deep technical expertise with team leadership, aligning product goals with reliable software architecture.

I focus on mentoring engineers, improving team delivery, and scaling web performance and conversion rates. Across Europe and Latin America, I have guided international squads, built e-commerce checkout platforms, and created open source developer tools.

📍 Berlin, Germany (Hybrid/Remote) 🗣️ Portuguese (Native), English (Advanced) 🎓 Degree in Systems Analysis (Positivo)

Career Journey

Professional Experience

Over 15 years of building web applications, leading engineering squads, and scaling digital experiences.

Lead Frontend Engineer • On

Berlin, Germany • Full-time

Current Role Nov 2024 – Present

Drive technical architecture for the global e-commerce platform. Lead server-side rendering (SSR) projects with edge caching to optimize Core Web Vitals. Refactor navigation systems and partner with product teams to deliver commercial features.

Senior Frontend Engineer & Engineering Manager • C&A Europe

Germany • Full-time

May 2023 – Nov 2024 • 1 yr 7 mos

Led digital projects and managed team deliverables across the e-commerce department. Led the migration of 15 million users to Auth0 under GDPR compliance. Guided the technical migration that decoupled authentication and wishlist services into AWS Fargate and Cloudflare microservices.

Co-Founder • Overdeck

Berlin, Germany • Remote • Self-employed

Indie Product Jan 2023 – Nov 2024 • 1 yr 11 mos

Co-founded and engineered Overdeck, a companion and controller ecosystem for content creators and streamers to engage audiences in real time. Architected and built the desktop application with Next.js, Node.js, and Electron, and mobile controller applications using React Native.

Senior Frontend Engineer • Trade Republic

Berlin, Germany • Full-time

May 2022 – Feb 2023 • 10 mos

Built reliable payment workflows and web interfaces in Vue.js and TypeScript for the Payments squad.

Senior Software Engineer • Contentful

Berlin, Germany • Full-time

Mar 2020 – Apr 2022 • 2 yrs 2 mos

Developed core platform features across the headless CMS product using React, TypeScript, and Node.js microservices.

Senior Frontend Engineer & Squad Lead • HelloFresh

Berlin, Germany • Full-time

Sep 2017 – Feb 2020 • 2 yrs 6 mos

Led the International Conversions squad of 7 frontend and backend engineers, directing team priorities and optimizing checkout conversion rates.

As a developer, built core React applications serving millions of monthly active users across 10 international markets.

Senior Frontend Engineer • EBANX

Greater Curitiba, Brazil • Full-time

Jul 2016 – Aug 2017 • 1 yr 2 mos

Built internal web applications using JavaScript, HTML5, and CSS3. The platforms served 20 million customers and processed payments across Latin America.

Frontend Engineer • Snowman Labs

Greater Curitiba, Brazil • Full-time

Jul 2015 – Jun 2016 • 1 yr

Built responsive web applications and mobile-first interfaces using JavaScript and modern browser standards.

Capabilities & Craft

Technical Matrix

A comprehensive toolkit spanning engineering leadership, frontend systems architecture, backend services, and product design.

⚡ Engineering • Frontend

React Vue.js Svelte TypeScript JavaScript HTML5 CSS Next.js Nuxt SvelteKit Storybook Tailwind Radix Vite Webpack Rollup Babel

🛠️ Engineering • Back-end & Systems

Node.js Deno Bun Golang Nest.js GraphQL REST APIs Microservices Clean Architecture

☁️ Engineering • Infrastructure

Terraform AWS Cloudflare Docker Kubernetes Digital Ocean CI / CD Pipelines

🧪 Engineering • Databases & Testing

Postgres MySQL MongoDB TypeORM Jest Vitest Cypress Playwright

🚀 Leadership & Delivery

Squad Leadership Technical Strategy & Roadmaps Engineer Mentorship Cross-Functional Delivery System Architecture Agile & Scrum Sprint Planning & Retrospectives

🎨 Design • UI & UX

Figma Interface Design Atomic Design Design System User Research Interviews Card Sorting User Flows Wireframes Paper Prototyping

🌍 Languages & Collaboration

Portuguese (Native) English (Advanced) Cross-Functional Teaming Remote & Hybrid Work

Open Source Ecosystem

Independent tools, packages & translations

A selection of open source libraries, indie web applications, and developer utilities I've built and maintained.

tinytivity

A zero-dependency, fully typed reactive state library for JavaScript and TypeScript. Published on JSR and compatible with all JavaScript runtimes.

JSR TypeScript

GitHub ↗

Pacenator

Running pace calculator and race time predictor. Converts speed and pace between metric and imperial units. Calculates finish times for 5K, 10K, half-marathon, and marathon distances.

tinytivity Vanilla JS

pacenator.com ↗

Overdeck

Companion & controller ecosystem for content creators and streamers. Built with Next.js, Node.js, and Electron for desktop, and React Native for mobile apps.

Next.js Node.js Electron React Native

overdeck.app ↗

react-fake-content

A lightweight, zero-dependency placeholder component library for React to render skeleton states during asynchronous data fetching.

NPM React

GitHub ↗

react-bucket-test

A React library to easily configure and run client-side A/B bucket tests with multi-provider tracking (e.g. Google Tag Manager).

NPM A/B Testing

GitHub ↗

share.it

A lightweight social share button component for Twitter, WhatsApp, Facebook, and LinkedIn.

JavaScript UI Widget

GitHub ↗

emojer.js

A JavaScript utility that converts ASCII emoticons like :) and :D into Unicode emoji.

String Parser JS

GitHub ↗

pozition.js

A TypeScript Promise wrapper for the browser Geolocation API with clean async/await coordinates access.

TypeScript Browser API

GitHub ↗

fogo

An experimental minimal web framework for lightweight Node.js web services and APIs.

Node.js Microframework

GitHub ↗

Academic Background

Education

Degree in Analysis and Systems Development

Positivo University • Paraná, Brazil

2011 – 2014