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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
Scroll down
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 Remote
Full-Stack Developer → Tech Lead · 2018 — 2026

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 and integrations
  • Performance and reliability improvements
  • CI/CD and production operations
  • Monitoring, observability and incident analysis
  • Mentoring and technical leadership
  • Systems handling global real-time traffic

Workfront (ProofHQ)

3 yrs 9 mos Remote
PHP Software Engineer II · May 2015 — Jan 2019

Worked as a backend PHP developer on an enterprise proofing and approval platform used by customers worldwide. Focused on scalable backend systems, API development, legacy modernization, search, analytics, automated testing and cross-team cooperation.

  • Backend development for an enterprise proofing and approval system
  • Over one year in the REST API team providing functionality for other product teams
  • Maintenance and improvement of SOAP APIs and the main web application
  • Handling client issues, SLA-related investigations and production bug fixes
  • Rewriting legacy code toward a separated frontend-backend architecture
  • Automated tests in Ruby Moto framework and unit tests in PHPUnit
  • Designed and implemented search based on Elasticsearch with MySQL fallback
  • Extended analytics system based on CQRS and Elasticsearch
  • Prepared proof of concepts for new product features
  • Cross-team cooperation in Scrum / Agile environment
  • Received Workfront distinctions in 2016 and 2017 for quality, ownership and taking on difficult challenges

Hoper Software

3 yrs 11 mos Lublin, Poland
Senior Software Development Engineer · Jun 2011 — Apr 2015

Worked as a full-stack developer and later senior/core technical team member on enterprise-class systems, including CRM, BPM, medical HIS and SaaS platforms. Combined software development with technical design, performance optimization, release management, client communication and project planning support.

  • Full-stack development of enterprise CRM, BPM, HIS and SaaS systems
  • CRM implementations based on SugarCRM for banking, art gallery and e-commerce use cases
  • Development of a flexible BPM workflow system for modeling business processes
  • Design and implementation of a medical HIS system with scheduling, medical history, prescriptions, services and settlement features
  • Redesigning SugarCRM-based architecture toward a SaaS model
  • Optimization of PHP modules, database queries, server layer and page rendering
  • Code quality supervision and technical guidance for the team
  • Production releases and deployment support
  • Integrations with external systems including HL7, SMS, cash registers and .NET applications
  • Supporting project planning through mockups, UML diagrams and technical analysis
  • Pre-implementation analysis, process identification and direct client communication

Make s.c.

1 yr 2 mos Lublin, Poland
Full-stack Developer · Apr 2010 — May 2011

Started professional software development as a junior/full-stack developer, working on ERP systems, e-commerce integrations and CMS-based landing pages while learning from experienced team members.

  • Development and deployment of ERP systems for customers in the agricultural industry
  • ERP modules for inventory, warehouse documents, invoices, HR and CRM
  • E-commerce development with integrations to external websites and data providers
  • Landing pages based on a company CMS
  • Gained practical full-stack development experience in a professional team environment
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.
// 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 tech lead roles.

My core stack is PHP and JavaScript/TypeScript — especially Laravel, Symfony, Vue, PostgreSQL, Docker, and AWS. I am also open to other technologies, including Python and .NET, especially in projects with strong engineering standards and meaningful business value.

I am particularly interested in roles where I can combine full-stack engineering experience with practical AI usage in development, automation, code analysis, prototyping, documentation, testing, and LLM-based product features.