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Hi! 👋

ŁukaszCieślicki

Senior Full-Stack Developer / Tech Lead

I build reliable web applications, modernize legacy systems, and help teams deliver scalable products.

15+
years of experience
Many
projects delivered
Tech Lead
who loves building teams
Łukasz Cieślicki
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01 // Who I am

About

I specialize in building and modernizing web applications, especially PHP-based systems with complex business logic, high traffic, and long-term maintainability requirements.

My strongest areas are backend architecture, clean code, performance optimization, API design, production infrastructure, observability, and AI-assisted development.

How I work

01
Pragmatic architecture
Right-sized design for the problem at hand — no speculative complexity.
02
Clean, maintainable code
Readable, tested, and built to be changed safely over years.
03
Production-first mindset
Shipping, deployment, and operability are part of the work, not an afterthought.
04
Observability, debugging & incidents
Structured logs, metrics, and calm incident analysis when things break.
05
Performance & reliability
Profiling, caching, and resilience under real production traffic.
06
Clear technical communication
Decisions, trade-offs, and risks written down and shared.
07
AI as an accelerator
AI speeds up the work — it never replaces engineering review.
08
Pragmatic learning
I pick up new technologies when they genuinely fit the product or team.
02 // Product mindset

Business & Product Understanding

I work comfortably with founders, product owners, and non-technical stakeholders — translating business goals into pragmatic technical decisions.

01
Business goal

Understand the outcome the organization needs.

02
Requirements

Clarify scope, constraints, and success metrics.

03
Trade-offs

Discuss options, risks, and delivery timelines openly.

04
Implementation

Build incrementally with quality and operability in mind.

05
Production feedback

Learn from real usage, metrics, and incidents.

Stakeholder communication

I explain technical choices in plain language and document decisions.

Product thinking

I focus on outcomes, not just tickets — balancing speed with maintainability.

Delivery partnership

I align engineering work with business priorities and realistic roadmaps.

03 // Selected work

Featured Projects

P01

ourRAG

A retrieval-augmented generation system for analyzing company documents and providing LLM-powered answers grounded in internal knowledge sources.

LLM RAG Embeddings Vector search Document ingestion Backend API
Engineering highlights
  • Document ingestion pipeline
  • Chunking & retrieval strategy
  • Source-grounded answers
  • Hallucination risk reduction
  • Internal knowledge search
P02

Web3 dApp

A Web3 application for connecting a MetaMask wallet and interacting with a local / test blockchain network.

TypeScript MetaMask Web3 Viem.sh Wagmi.sh Local chain Smart contracts
Engineering highlights
  • Wallet connection
  • Network detection
  • Account switching
  • Reading on-chain data
  • Sending test transactions
P03

Darts Scorekeeper

A local-first mobile app for tracking darts games, player scores, turns, busts, checkout rules, and match statistics.

React Native Expo Local-first Mobile UX
Engineering highlights
  • 301 / 401 / 501 game modes
  • Double-in / double-out rules
  • Fast score input for small screens
  • Local-first architecture
  • Match statistics
04 // Career

Commercial Experience

Flightradar24

7+ yrs
Full-Stack Developer → Tech Lead · 2018 — Present

Worked on high-traffic aviation systems used globally. Contributed to legacy modernization, frontend rewrites, API development, production operations, performance improvements, CI/CD, and technical leadership.

  • Modernization of legacy PHP / jQuery systems
  • Vue / TypeScript frontend work
  • API architecture & integrations
  • Performance & reliability improvements
  • CI/CD & production operations
  • Mentoring & technical leadership
  • Systems handling global real-time traffic

Earlier commercial projects

8 yrs
Earlier commercial experience · Before 2018

Enterprise web systems, approval workflows, REST / SOAP integrations, search, analytics, and backend-heavy applications.

  • Enterprise web systems
  • Approval workflows
  • REST / SOAP integrations
  • Search & analytics
  • Backend-heavy applications
05 // Toolbox

Tech Stack

SRE

SRE / Observability

I have practical experience with production monitoring, observability, incident analysis, and performance troubleshooting. I have worked with tools such as Datadog, New Relic, and Logstash to understand system behavior, detect issues, analyze incidents, and improve reliability.

01

Backend

PHP Laravel Symfony Node.js REST APIs Domain modeling RabbitMQ Kafka
02

Frontend

TypeScript Vue.js React.js Tailwind CSS Vite Inertia SPA/SSR
03

Databases

MySQL PostgreSQL Amazon Aurora Redis Elasticsearch
04

Infrastructure / DevOps

AWS Docker Kubernetes Terraform Cloudflare Nginx Traefik
05

CI/CD

GitHub Actions Jenkins Blue-Green Deployments Canary Releases
06

SRE / Observability

Datadog New Relic Logs Metrics Tracing OpsGenie
07

Architecture

SOLID Clean code Service layer Modular architecture Event-driven Performance optimization
08

AI / Tools

OpenAI Codex Claude Code Cursor Figma AI MCP RAG
09

Currently learning

Python AI / LLM engineering Automation Backend tooling Data processing basics
06 // Depth

Case Studies

01
Product idea
A social platform for non-monetary bets: people stake reputation, not money, and resolve outcomes together.
02
Domain model
Bets, beliefs, invites, resolutions, reactions and subscriptions modeled as an explicit, testable core.
03
Laravel backend
Service-layer architecture, queues, policies and a clean API powering the Inertia frontend.
04
Vue / Inertia frontend
A single cohesive app — server-driven routing with reactive Vue 3 + TypeScript components.
05
PostgreSQL / Redis
Relational integrity in Postgres; Redis for cache, sessions, and queue backing.
06
Queues & notifications
Async jobs for notifications, OG image generation, and trending computation.
07
Docker / VPS deployment
Containerized stack deployed to a VPS with reproducible builds.
08
Cloudflare, Traefik, blue/green
Edge protection, automatic routing, and zero-downtime blue/green releases.
01
Document ingestion
Pipelines that normalize and index heterogeneous internal documents.
02
Chunking
Content split into semantically meaningful chunks tuned for retrieval quality.
03
Retrieval
Vector search surfaces the most relevant passages for each query.
04
Prompt design
Prompts that constrain the model to provided context and structure.
05
Source-based responses
Every answer cites the documents it was grounded in.
06
Trustworthy AI answers
Hallucination risk reduced by grounding and explicit 'not found' handling.
01
Incremental refactoring
Small, safe steps behind tests instead of risky big-bang rewrites.
02
Replacing procedural / jQuery code
Moving toward structured services and a modern Vue frontend.
03
Improving maintainability
Clearer boundaries, naming, and tests that make change cheaper.
04
Reducing operational risk
Fewer surprises in production through observability and guardrails.
05
Keeping product moving
Feature work continued in parallel with modernization.
08 // Résumé

Curriculum Vitae

Download CV (PDF)
Łukasz Cieślicki
Senior Full-Stack Developer / Tech Lead
cieslicki.lukasz@gmail.com github linkedin

Summary

Senior Full-Stack Developer and Tech Lead with 15+ years of commercial experience, including 7+ years at Flightradar24. I build, modernize, deploy, monitor, and maintain PHP / Laravel / Vue products end-to-end — backend architecture, frontend, infrastructure, and SRE-oriented production operations. Currently learning Python and AI/LLM engineering; open to growing into new stacks.

Experience

Flightradar24 2018 — Present
Full-Stack Developer → Tech Lead
  • Modernization of legacy PHP / jQuery systems
  • Vue / TypeScript frontend work
  • API architecture & integrations
  • Performance & reliability improvements
Earlier commercial projects Before 2018
Earlier commercial experience
  • Enterprise web systems
  • Approval workflows
  • REST / SOAP integrations
  • Search & analytics

Selected projects

  • BetOnBeliefs — social betting platform (Laravel 12, Vue 3)
  • OurRAG — retrieval-augmented document Q&A
  • Web3 dApp — MetaMask wallet integration
  • Darts Scorekeeper — local-first React Native app
  • MCP Betting Generator — AI tool integration

Skills

Backend
PHP · Laravel · Symfony · Node.js · REST APIs · Domain modeling · RabbitMQ · Kafka
Frontend
TypeScript · Vue.js · React.js · Tailwind CSS · Vite · Inertia · SPA/SSR
Databases
MySQL · PostgreSQL · Amazon Aurora · Redis · Elasticsearch
Infrastructure / DevOps
AWS · Docker · Kubernetes · Terraform · Cloudflare · Nginx · Traefik
CI/CD
GitHub Actions · Jenkins · Blue-Green Deployments · Canary Releases
SRE / Observability
Datadog · New Relic · Logs · Metrics · Tracing · OpsGenie
Architecture
SOLID · Clean code · Service layer · Modular architecture · Event-driven · Performance optimization
AI / Tools
OpenAI Codex · Claude Code · Cursor · Figma AI · MCP · RAG
Currently learning
Python · AI / LLM engineering · Automation · Backend tooling · Data processing basics

Education & courses

  • Aidevs.pl course
  • Droganowoczesnegoarchitekta.pl course
  • AI-assisted software development
  • Practical experiments with Codex, Claude, Cursor, Figma & GitHub Spec Kit
  • Agile/Scrum Course
  • PRINCE2 Foundation Certificate
  • Practical Experiments with Codex, Claude, Cursor, Figma, and GitHub Spec Kit
  • Master's Degree in Computer Science, Lublin University of Technology

Languages

  • Polish — Native
  • English — Professional working proficiency
// Direction

Beyond my main stack

My strongest background is PHP, Laravel, Symfony, Vue, TypeScript, and production infrastructure. At the same time, I actively expand beyond this stack. I am currently learning Python and exploring AI/LLM engineering, automation, and backend tooling. I am open to roles where I can bring senior engineering experience while growing into a new technology stack.

Currently learning
Python AI / LLM engineering Automation Backend tooling Data processing basics

I am currently learning Python to broaden my backend and AI engineering capabilities. My goal is to use Python mainly for automation, AI/LLM integrations, backend tooling, data processing, and scripting.

Open to new technologies

Although my strongest commercial background is in PHP, Laravel, Symfony, Vue, and JavaScript, I am open to switching technologies when the project is interesting and the engineering culture is strong. I learn new stacks pragmatically, focusing first on architecture, product needs, code quality, performance, and maintainability.

// Get in touch

Let's talk

Available for remote senior full-stack, backend, Laravel / PHP, and technical lead roles.

Preferred stack
PHP / Laravel / Symfony / Vue / TypeScript / PostgreSQL / Docker / AWS