Julien is available for hire

Julien Demarque

Verified Expert in Engineering

Full-stack Engineer and Developer

Tel Aviv-Yafo, Israel

Toptal member since May 22, 2026

Expertise

Front End Startup Development Full-stack Back-end Developers Artificial Intelligence LLM RAG Chatbot Development React.js TypeScript JavaScript CSS JSON

Bio

Julien is a full-stack engineer with 7+ years of experience building scalable back-end, front-end, and AI systems. He owns end-to-end products, from architecture to production, and focuses on reliability and real-world impact. Julien has recently worked on agentic AI, RAG pipelines, and workflow automation systems that reduce manual work and accelerate delivery.

Portfolio

Invisible Technologies

TypeScript, Python, React, Next.js, Apache Kafka, AI Engineering...

Experience

TypeScript - 7 years
React - 7 years
PostgreSQL - 5 years
Python - 5 years
Next.js - 5 years
AI Engineering - 3 years
LLM Integration - 3 years
Model Context Protocol (MCP) - 2 years

Preferred Environment

Python, React, LangChain, Next.js, LLM Integration, TypeScript, PostgreSQL, Apache Kafka, Google Cloud Platform (GCP), AI Engineering

The most amazing...

...system I've built merges AI with workflow automation, turning natural language into production-ready workflows in minutes.

Work Experience

Software Engineer

2019 - 2026

Invisible Technologies

Built and scaled a workflow automation platform with human-in-the-loop capabilities, enabling cross-functional teams to design and operate complex processes in production.
Designed and deployed AI systems that convert natural language into executable workflows, reducing setup time from hours to minutes and improving operational efficiency.
Engineered real-time data pipelines using Kafka and WebSockets to power live dashboards, enabling instant updates and improving decision-making speed.

Technologies: TypeScript, Python, React, Next.js, Apache Kafka, AI Engineering, Google Cloud Platform (GCP), Django, FastAPI, Model Context Protocol (MCP), PostgreSQL, Docker, Redis, Temporal, Celery, Playwright, JavaScript, RAG Systems, LangChain, LlamaIndex, Agentic AI, Auth0, MongoDB, Node.js, Prisma, LLM Integration, AI/ML Workloads, Agentic RAG Systems, Scalable Vector Databases, Artificial Intelligence (AI), Large Language Models (LLMs), Vector Databases, Retrieval-augmented Generation (RAG), Vercel, AI Tools, APIs, Agentic AI Systems, CSV, Agile, Minimum Viable Product (MVP), Product Requirements Documentation (PRD), Product Management, Software Architecture, Software Design, Project Management, Documentation, Cybersecurity, Harness, LangGraph, AI SDK, OpenAI Assistants API, Datadog, AI Agent Orchestration, AI Agents, Semantic Search, Workflow Automation, REST APIs, Workflow Automation & System Integration, n8n, Full-stack, DB, Express.js, Full-stack Development, Authentication, Prompt Engineering, CI/CD Pipelines, Zod, OpenAI, Debugging, SVG, API Integration, Tailwind CSS, Firebase, Architecture, RAG Pipelines, Generative Artificial Intelligence (GenAI), RAG Architecture, Vector Search, Data Engineering, SQL, Large Language Model Operations (LLMOps), Natural Language Processing (NLP), OpenAI API, AI Integration, RESTFul APIs, Amazon Web Services (AWS), Asyncio, Pydantic, Chatbot Conversation Design, Chatbots, Technical Leadership, GitHub, Back-end, Front-end, GitHub Actions, Startups, REST, GraphQL, Supabase, Vite, PDF, Open-source LLMs, Model Evaluation, Document Processing, Bash, AI Development, Cloud Infrastructure, Automation, Bash Script, CSS, Bedrock, Anthropic, DevOps, Google Drive API, Image Processing, AI Automation, Data Architecture, Scripting, Synthetic Data Generation, Security, WebSockets, RabbitMQ, React Query, React Router, Amazon Bedrock, Redux, HTML, Cursor AI, JSON, OAuth, Webhooks, OpenAPI, Swagger, SQLAlchemy, Azure, Langfuse, Role-based Access Control (RBAC), Authorization, Workflows, Cloud Architecture, Dashboards, Computer Vision, System Architecture, Multi-agent Systems, React Testing Library, Webpack, AI-generated Code, TanStack Router, Claude Code, API Development, Agentic Frameworks, Agentic Coding, Telemetry, Monitoring, Kubernetes, SDKs, Tailwind UI, Real-time Systems, Heroku

Experience

JobSearchAgent

https://github.com/JulienDemarque/JobSearchAgent

A personal AI job search and opportunity tracker built around LangChain, LangGraph, LangSmith, FastAPI, PostgreSQL, and a custom Agent Chat UI workspace.

The app allows users to chat with an agent while keeping a structured opportunities table as the source of truth for roles, links, fit scores, application status, interview state, and notes.

Secure LLM Gateway

https://github.com/JulienDemarque/secure-llm-gateway

I built a production LLM API security gateway with authentication, rate limiting, threat detection, PII handling, output validation, and audit logging. Routes require hashed API keys stored in MongoDB with role-based middleware, including an admin-only /v1/audit endpoint. Redis enforces per-key sliding-window limits (default: 30 requests per minute). Inbound chat requests are classified for prompt injection, with detected threats returning a 400 response. PII is tokenized with encrypted span storage for authorized audit replay. Outbound responses are checked for secret leakage and prompt injection echoes, while PII is redacted before being returned. Each /v1/chat call logs hashes, latency, status, and threat metadata in MongoDB, linked through correlation IDs. Provider secrets remain in environment variables, and gitleaks and CI pipelines prevent committed secrets.

Certifications

MAY 2026 - PRESENT

Supervised Machine Learning: Regression and Classification

Stanford University

Skills

Libraries/APIs

React, Node.js, REST APIs, React Query, React Router, API Development, Zod, OpenAI API, Asyncio, Pydantic, OpenAPI, SQLAlchemy, React Testing Library, Playwright, OpenAI Assistants API, Google Drive API

Tools

Docker Compose, AI SDK, n8n, GitHub, Webpack, TanStack Router, Claude Code, Celery, Auth0, Prisma, RabbitMQ

Languages

Python, TypeScript, JavaScript, GraphQL, CSS, HTML, SQL, Bash, Bash Script

Frameworks

Next.js, LlamaIndex, Tailwind CSS, Agentic Frameworks, Django, Express.js, LangGraph, Redux, Swagger, Bedrock

Paradigms

REST, Automation, Model Context Protocol (MCP), Agile, Synthetic Data Generation, Role-based Access Control (RBAC), Real-time Systems, DevOps

Platforms

LangSmith, Docker, Harness, Amazon Web Services (AWS), Heroku, Apache Kafka, Google Cloud Platform (GCP), Vercel, Ollama, Firebase, Azure, Langfuse, Kubernetes

Storage

JSON, PostgreSQL, MongoDB, DB, Redis, Datadog

Industry Expertise

Project Management, Cybersecurity

Other

LangChain, LLM Integration, AI Engineering, FastAPI, RAG Systems, Agentic AI, Agentic RAG Systems, Artificial Intelligence (AI), Large Language Models (LLMs), Retrieval-augmented Generation (RAG), APIs, Agentic AI Systems, AI Agent Orchestration, AI Agents, Semantic Search, Workflow Automation, Workflow Automation & System Integration, Full-stack, Full-stack Development, API Integration, Architecture, RAG Pipelines, RAG Architecture, Vector Search, RESTFul APIs, Chatbot Conversation Design, Chatbots, Back-end, Front-end, GitHub Actions, Startups, Model Evaluation, AI Development, AI Automation, Cursor AI, Workflows, Multi-agent Systems, AI-generated Code, Tailwind UI, Zustand, Scalable Vector Databases, Vector Databases, AI Tools, CSV, Minimum Viable Product (MVP), Product Requirements Documentation (PRD), Product Management, Software Architecture, Software Design, Documentation, Authentication, Prompt Engineering, CI/CD Pipelines, OpenAI, Debugging, SVG, Generative Artificial Intelligence (GenAI), Large Language Model Operations (LLMOps), Natural Language Processing (NLP), AI Integration, Technical Leadership, Vite, PDF, Open-source LLMs, Document Processing, Cloud Infrastructure, Anthropic, Image Processing, Data Architecture, Scripting, Security, WebSockets, OAuth, Webhooks, Authorization, Cloud Architecture, Dashboards, System Architecture, Agentic Coding, Telemetry, Monitoring, SDKs, Temporal, AI/ML Workloads, Supervised Machine Learning, Linear Regression, Logistic Regression, Machine Learning, Data Engineering, Supabase, Amazon Bedrock, Computer Vision

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