Senior Full Stack Engineer, AI Applications

Sebastian Leal

Redondo Beach, CA *********.****.*********@*****.*** +1-424-***-**** https://www.linkedin.com/in/sebasleal Senior Full Stack Engineer

Senior Full Stack Engineer with 8+ years of experience building scalable web applications using Python, React, Next.js, and Node.js. Experienced in designing REST APIs, modern frontend architectures, cloud deployment, and AI-powered applications using OpenAI and LangChain. Focused on building reliable software that improves user experience and solves real business problems.

Core Competencies

Full-stack Development API Design & Integration AI Solutions Responsive UI/UX State Management (Redux, Context API, Zustand) Authentication & Security Database Management Performance Optimization Testing & Debugging Agile Methodologies Version Control (Git, GitHub) CI/CD Pipelines & Automation Third-Party API Integration Code Review & Best Practices Problem-Solving Technical Skills

Programming Languages: JavaScript, TypeScript, Python, HTML5, CSS3 Frontend Technologies: React.js, Next.js, Vue.js, Nuxt.js, Tailwind CSS, Redux, Zustand, Axios AI Technologies: OpenAI, LangChain, LangGraph, Vapi, Anthropic, AI Chatbots, Image Generation, RetellAI Backend & API Development: Node.js, Express.js, NestJS, Python (Django, Flask), RESTful APIs, GraphQL, Bcrypt, JSON Web Tokens (JWT), Docker

Database Management: PostgreSQL, MySQL, MongoDB, Firebase, Firestore, Supabase Cloud & DevOps: Docker, AWS (EC2, S3, RDS), Google Cloud Platform (GCP), Firebase Functions, CI/CD

(GitHub Actions)

Testing & Debugging: Test-Driven Development (TDD), Mocha, Playwright, Jest, Pytest, Nose, Cypress Version Control & Collaboration: Git, GitHub, GitLab, Agile/Scrum, Trello, Notion EXPERIENCE & KEY PROJECTS

Senior Full Stack Developer

Train children Chess Academy Los Angeles, CA 2021 – Present

Developed five production web applications using TypeScript, React (later migrated to Next.js), Python (Django), Node.js, and PostgreSQL.

Built high-performance backend services using Node.js, Express, NestJS, and Django, designing scalable RESTful APIs and GraphQL endpoints supporting high-volume production workloads.

Integrated OpenAI, LangChain, LangGraph, and Vapi to build AI assistants, document- processing workflows, content generation tools, and voice-enabled features.

Improved chatbot response accuracy by 35% using LangChain and Retrieval-Augmented Generation (RAG).

Designed and optimized complex PostgreSQL database schemas, improving query performance by 55% through indexing and query optimization.

Containerized applications with Docker, enabling consistent local development and production deployments.

Developed automated test suites using Jest, Playwright, and Pytest, reducing regressions and improving release confidence.

Implemented CI/CD pipelines to automate testing, build validation, and deployment, reducing deployment time by 70% while improving release reliability.

Implemented authentication, cloud storage, notifications, and real-time synchronization using Firebase Authentication and Firestore.

Reduced page load times by 35% through code splitting, lazy loading, caching strategies, GraphQL query optimization, and frontend performance tuning.

Full Stack Developer

Playworks Los Angeles, CA 2018 – 2020

Developed and maintained full-stack web applications using Python, MySQL, React.js, HTML5, CSS3, JavaScript, and GitHub, supporting internal operations and administrative workflows.

Modernized legacy applications by upgrading traditional HTML and JavaScript pages into reusable React.js components, improving maintainability, user experience, and development efficiency.

Reduced CSS maintenance by 40% through reusable components.

Built responsive, mobile-friendly interfaces using React.js, CSS3, and modern frontend techniques, ensuring consistent functionality across major browsers and devices.

Implemented WebSocket-based real-time features for dashboards and notifications while optimizing backend queries and frontend rendering to improve overall application performance.

Collaborated with cross-functional teams using GitHub version control, performed code optimization, resolved production issues, and contributed to continuous enhancements of existing systems.

Assisted in database design and maintenance using MySQL, writing optimized SQL queries and improving data integrity across internal systems.

EDUCATION

Bachelor’s degree

California State University, Long Beach 2015 – 2018

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