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Sergiu LefterSoftware engineerBucharest, Romania

Turning ideas into useful software.

Currently

Software Engineer | Mobile & Web
at SeaCortex.

I enjoy working through interesting problems, understanding how things work, and learning along the way.

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02Work experience

Built in production.

Recent work across mobile applications, data, and the web.

Mar 2026 — Present

SeaCortex

Bucharest · On-site

Software Engineer | Mobile & Web

  • Build cross-platform mobile applications with React Native, Expo, and TypeScript — reusable interfaces, authentication flows, and API integration.
  • Reduced median React render counts by 35.7% in controlled Android profiling, alongside work on background location tracking, offline access, and platform-specific reliability.
  • Ship offline-first data layers with bundled SQLite, map systems using Mapbox and H3 spatial indexing, and health-data integration through HealthKit and Health Connect.
  • Work on AI-powered product features: streaming responses, retrieval-augmented generation, automated validation, and internal review tooling.
  • Build geospatial processing pipelines in Python for nationwide demand-based classification.
  • React Native
  • Expo
  • TypeScript
  • Firebase
  • SQLite
  • Mapbox
  • H3
  • Python
  • Zustand

Jun 2025 — Mar 2026

Verasys

Bucharest · Hybrid

Full Stack Developer

  • Developed reusable UI components from Figma designs using Next.js, React, and Tailwind CSS, building scalable interfaces for an e-commerce platform.
  • Integrated REST APIs and Payload CMS, and optimized database import processes to improve data consistency and reduce execution time.
  • Next.js
  • React
  • Tailwind CSS
  • Payload CMS
  • REST APIs
03Projects

The decisions behind the software.

Selected projects, with the constraints and engineering decisions that shaped them.

Case 01Team / Backend & B2B platform

hai

An app for making plans with friends, with a business platform for venues to publish events and offers.

Constraint
Connect friends and venues while keeping social data private and business actions scoped to the right people.
Implementation
Hardened the Supabase backend and built the Next.js B2B platform, covering business onboarding, publishing, admin tools, and staff-confirmed QR redemption.
Next.js · TypeScript · Supabase · PostgreSQL
Case 02Team / Backend

MemoTap

Voice-first reminders — speak naturally, and the app works out what you meant.

Constraint
Turn natural-language requests into structured reminders that can be scheduled.
Implementation
Built the Express API and MongoDB data layer, with Gemini API intent understanding.
Recognition
2nd place at JA Innovation Camp 2025.
React Native · Expo · Node.js · Express.js

More projects

Selected builds and experiments

emu8086-web

Browser-based Intel 8086 assembler, emulator, and debugger. Run assembly programs and inspect registers, memory, and execution step by step, with no installation.

TypeScript · React · Vite

Gamster Bot

Moderation platform for the Gamster Minecraft community Discord server.

Node.js · Discord.js v14 · MongoDB

Wrdl Bot

Wordle for Discord, playable on any server.

Node.js · Discord.js v14

SkyKit Optimizer

Airline rotables logistics optimizer, built in 48 hours.

HackITAll 2025 · SAP 48H — 8th place, Honorable Mention for engineering quality

TypeScript · Node.js · React

Medical Correct Solution

Multi-role medical application for administrators, doctors, and patients.

Flutter · Dart · Firebase
04About & Awards

Curiosity, beyond the screen.

I am a software engineer in Bucharest, currently building cross-platform mobile applications at SeaCortex. I enjoy the parts of a product that become difficult outside a prototype: offline access, background behavior, performance, and the systems behind the screen.

I study Computer Engineering at the University Politehnica of Bucharest, specializing in Internet of Things (IoT). I am interested in how software connects with sensors, devices, and the physical world. Competitive programming first drew me to engineering, and I still like work with a real constraint.

I am also interested in cybersecurity and keep learning about it outside my day-to-day work.

Recognition & involvement

Beyond day-to-day work
1st place2026

JA Innovation Camp with HP

Co-developed and presented GreenCampus, a sustainable campus concept combining an app for green activity rewards, air-quality monitoring, and a supporting business model.

2nd place2026

Scientific Communication Session in Software Engineering & AI

University Politehnica of Bucharest

2nd place2025

JA Innovation Camp

Developed and presented MemoTap, a voice-first reminder application, as a team.

05Contact

Let's talk.

Want to discuss mobile engineering, a project, or something I have built? Send me an email.

Elsewhere