Md Maruf Billah
Lead Software Engineer · Full-Stack (JavaScript & TypeScript)
Open to on-site roles - in Bangladesh or relocating abroad
Profile
Lead Software Engineer with 5+ years shipping production web platforms in JavaScript and TypeScript for clients in France, the UK and Germany. I lead a team of 10 and still write a large share of the code - React and Next.js, Node.js and NestJS, PostgreSQL, and AWS/Azure with CI/CD - and I'm known for owning hard problems end to end, from sync and KPI engines to a double-entry wallet and crash-safe checkout.
Key achievements
- Shipped 1,500+ A/B experiments for 20+ brands of a global luxury group over 3 years.
- I lead 10 engineers and am a joint top contributor to the company HR platform's React front end (268 of 973 commits, 150+ merged PRs).
- Built a QA analytics platform almost alone: ~120k lines, 59 data models, 92-97% of commits.
- Built the company's A/B tooling: ABTestPilot, used company-wide for 3 years, and ABTestLab, an open-source CLI now adopted company-wide.
Core skills
- Languages
- JavaScript (ES6+), TypeScript, SQL, HTML5, CSS3 / Sass, Java, Python
- Front end
- React, Next.js, Redux Toolkit, Redux-Saga, Zustand, TanStack, Tailwind CSS, MUI, shadcn/ui, GSAP, PWA
- Back end
- Node.js, NestJS, Express, REST + Swagger, WebSockets (Socket.IO), background jobs (BullMQ, pg-boss), integrations and middleware
- Cloud & DevOps
- AWS (Lambda, EC2, ECS, S3, SES, CloudWatch, Amplify, Lightsail), Azure (Blob Storage, Communication Services), Docker, GitHub Actions CI/CD, Vercel
- Data
- PostgreSQL, MySQL, DynamoDB, Firestore, Supabase; Prisma, TypeORM, Drizzle ORM
- Security & quality
- Entra ID (MSAL), OAuth 2.0, JWT, OTP, RBAC, AES-256-GCM, audit logging; Vitest, Jest, Playwright, Supertest
- Experimentation
- VWO, AB Tasty, Optimizely, Dynamic Yield, Kameleoon, Convert
- Leadership
- Leading 10 engineers, architecture, estimates, code review, mentoring, client communication
Professional experience
Lead Software Engineer · Echologyx Ltd
2022 - Present- Lead a team of 10 engineers: technical design, code review and merges, estimates, mentoring and client calls.
- Built ABTestLab (open-source A/B test CLI) and moved the agency's 1,700-experiment monorepo onto it; with ABTestPilot it is the team's standard tooling.
Global luxury group (France) - Front-End Engineer, A/B/n experimentation
2022 - 2025- Built and shipped 1,500+ A/B/n experiments across 20+ luxury e-commerce brands, working daily with the client's optimisation team in France.
- Delivered product and gift finders, size guides, checkout redesigns and animated campaigns with performance-safe DOM injection across markets.
Stack: JavaScript, SCSS, GSAP, VWO, AB Tasty, Dynamic Yield, Kameleoon, GitHub Actions
eHRMS - company employee-management platform - Lead Full-Stack Engineer
2023 - Present- Company-wide platform for leave, holidays, profiles, calendars, shifts, KPIs and time tracking; joint top contributor to the React front end (268 of 973 commits, 150+ merged PRs) and third-highest on the NestJS API.
- Delivered the KPI module end to end (UI and API): goal templates, review periods, monthly scoring, permissions and dashboards; added Microsoft Entra ID SSO and partner APIs for leave data.
- Serverless API on AWS Lambda with CloudWatch, S3 storage, SES/SMTP email and a GitHub Actions staging pipeline with smoke tests.
Stack: React, TypeScript, Redux-Saga, MUI, NestJS, TypeORM, PostgreSQL, AWS Lambda, S3
European CRO agency (Germany) - Full-Stack Engineer, QA & performance analytics
2025 - 2026- Built the QA and performance-analytics platform almost single-handedly (92-97% of commits, ~120k lines): NestJS API with 59 data models and 38 modules, React 19 front end, on AWS EC2 and Lambda with SES/SMTP and GitHub Actions CI/CD.
- Engineered a Jira-to-PostgreSQL sync engine (full, incremental and webhook modes, idempotent mapping, per-config cron, live WebSocket progress, AES-256-GCM-encrypted tokens).
- Designed a configurable KPI system: 14 KPI equations, a JSONB bug-scoring rule engine, hours-share ticket attribution, cached leaderboards and target boards; Slack bot and HR-system integration.
Stack: NestJS 11, Prisma 7, PostgreSQL, Socket.IO, React 19, TanStack, AWS EC2, Lambda
UK retail group - Full-Stack Engineer, integration middleware
2026- Built middleware connecting the main business application with the warehouse application, with a React (Vite) front end on a large MySQL database.
- Migrated application logic from Ruby to JavaScript; containerised with Docker and deployed on AWS ECS with CI/CD on GitHub Actions.
Stack: React, Vite, Node.js, MySQL, Docker, AWS ECS
Internal and client products
2025 - 2026- ELX Project Management Tool: 103 of 167 commits of an Asana-style app with realtime collaboration, RBAC and a CRO module.
- Service Pro Plus (UK client): most of a garage directory and review platform with OTP login and Maps search, on AWS and Azure.
- Tour Console (sole developer): the company's annual-tour app - tournaments, roommate matching, polls, moderated feed - plus a React Native app.
Stack: Next.js, Prisma, PostgreSQL, Firebase, Socket.IO, AWS (Amplify, EC2, S3, SES), Azure, Docker
Lead Full-Stack Engineer · Travel and hospitality group (confidential)
2024 - Present- Designed and built the API for a 9-vertical travel super-app as a NestJS modular monolith: 70 data models, ~236 endpoints and ~550 unit tests.
- Built a double-entry ledger and wallet with row-locked balance checks and an idempotent checkout saga with compensation, so multi-supplier orders recover after a crash.
- Added resilient supplier integrations (circuit breakers, backoff), a 75-page React app, EC2 deploys that snapshot the database before migrating, and the group's corporate website.
Software Engineer · Nexkraft Limited
2021 - 2022- Developed Android applications in Java, including a transport-management app for BRAC.
Selected projects
- AI Job Finder (Next.js 16, Prisma 7, PostgreSQL, pg-boss, Gemini) - Job search and outreach platform with 9-factor + LLM ranking, visa-sponsor checks and a self-checking email pipeline (~29k lines, 147 tests).
- ABTestLab (Node.js, WebSocket, Rollup, Sass) - Open-source CLI to build and live-preview A/B tests for any platform; adopted company-wide (192 commits).
- TrustPortal, ShadowFeed, TournaTrack (Next.js, Prisma, Firebase) - An interaction-design concept site, an anonymous moderated company feed, and the tournament app that became Tour Console.
Education
BSc in Computer Science and Engineering
2021Capstone: Shikkha, an LMS with WebRTC video classes (136 of 233 commits, team of 4).
Courses: The Ultimate React Course, Advanced CSS and Sass, Complete Node.js Bootcamp, The Complete JavaScript Course
Languages
- BengaliNative
- EnglishC1 - full professional (CEFR)
References
10 recommendations from managers, clients and colleagues on LinkedIn (linkedin.com/in/marufbillah1020). References available on request.