Mark – Python, React, Next.js, experts in Lemon.io

Mark

From Brazil (UTC-4)flag

Full-stack Web Developer|Senior
Back-end Web Developer|Strong senior
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Mark – Python, React, Next.js

Mark is a Senior Full-Stack Engineer with 8 years of experience, specializing in Python and React with deep hands-on expertise in AI/LLM systems. He's currently building production multi-agent educational platforms using LangChain, LangGraph, WebRTC, and OpenAI — owning everything from architecture to cloud deployment on AWS and GCP. Mark doesn't just implement features; he connects technical choices to product outcomes, designs infrastructure from scratch, and ships without close supervision — a strong fit for AI-first startup teams that need engineers who take real ownership.

8 years of commercial experience in
AI
Edtech
Energy
Fintech
Renewable energy
Open source
Enterprise software
SaaS
Main technologies
Python
8 years
React
5 years
Next.js
3 years
AWS
4 years
Typescript
4 years
Additional skills
GraphQL
WebRTC
FastAPI
GCP
Golang
OpenAI
PostgreSQL
AWS CloudFormation
AWS Lambda
Cognito
IoT
DynamoDB
Redis
D3.js
Unit testing
UI/UX
WordPress
Design system
Usability testing
Webflow
LLM
Django
Kubernetes
Direct hire
Possible
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Experience Highlights

Senior Software / AI Engineer
Jul 2025 - Ongoing1 year
Project Overview

Speech-to-speech conversational learning tool (LTI) embedded in an LMS, built for AI-driven educational interactions. The platform supports multi-agent Dialogue flows, real-time voice and text sessions over WebRTC, document-aware tutoring with in-session RAG, and AI-generated Key Moments for post-session review. Deployed on AWS and GCP with full accessibility (ARIA/WCAG) compliance.

Responsibilities:
  • Architected multi-agent AI systems using LangChain, LangGraph, and OpenAI — enabling real-time user-to-agent voice and text interactions via WebRTC with supervisor/worker agent patterns
  • Replaced Whisper-based transcription with a custom decoupled layer that preserved accuracy when agents were interrupted; added timestamp-based message sorting across LTI and LMS sessions
  • Implemented in-memory vector stores with OpenAI Embeddings and pgvector for near-zero-latency real-time RAG over session-bound, multi-source documents
  • Built the Dialogue system — a multi-step, context-carrying multi-agent framework with shared conversation history, a sequence builder for assignment types, and AI-generated Key Moments for post-session review
  • Instrumented LLM pipelines with Langfuse for end-to-end tracing, latency profiling, and token usage optimization across multi-agent production flows
  • Deployed AI-powered services end-to-end (Python/FastAPI, Go/GORM, Next.js) on AWS and GCP, from architecture through production monitoring
Project Tech stack:
Python
FastAPI
Golang
Next.js
AWS
GCP
GraphQL
OpenAI
LangChain
LangGraph
RAG
WebRTC
Full-Stack Engineer
Aug 2024 - Ongoing2 years
Project Overview

Personal finance management app for tracking expenses, income, and financial goals, with interactive dashboards and data visualizations. Full-stack open source project with production-grade security architecture.

Responsibilities:
  • Built a full-stack finance tracker with a Next.js 15 / React 19 frontend and NestJS REST API backend backed by PostgreSQL
  • Implemented interactive charts and expense visualizations using Chart.js
  • Set up JWT authentication with CSRF double-submit cookie protection, Helmet headers, rate throttling, and input sanitization
  • Containerized the full application with Docker Compose for reproducible local and deployment environments
  • Maintained 215+ commits with branch-based workflow, PR reviews, and documented architecture
Project Tech stack:
Next.js
React
Typescript
Nest.js
Node.js
PostgreSQL
Docker
JWT
Tailwind CSS
Software Engineer
Apr 2022 - Apr 20242 years
Project Overview

Energy management software for a transformer monitoring system (SMT) at one of the world's largest power plants. The platform tracked real-time sensor data from high-voltage transformers, with strict zero-downtime and regulated testing requirements.

Responsibilities:
  • Refactored an IoT anomaly detection system with AI-driven predictive analysis, improving fault detection accuracy for high-voltage transformer monitoring
  • Built serverless and microservices architectures on AWS (Lambda, DynamoDB, S3, EventBridge) processing real-time sensor data streams via Kafka
  • Developed real-time data visualization dashboards for the Energy Management sector using Next.js and D3.js
  • Optimized PostgreSQL queries and Redis caching layer, reducing system latency by 13%
Project Tech stack:
AWS Lambda
DynamoDB
Amazon S3
Apache Kafka
Next.js
D3.js
PostgreSQL
Redis
Typescript
IoT
Java
Python
Golang
React
Software Engineer
Dec 2020 - Mar 20221 year 2 months
Project Overview

Internal tooling team focused on Node.js ecosystem modernization and CI/CD infrastructure. Worked on migrating JavaScript codebases to TypeScript and improving developer tooling used by tens of thousands of engineers daily.

Responsibilities:
  • Wrote unit and integration tests for an internal CI/CD system on the Node.js tooling team, achieving 95% test coverage
  • Implemented a Redis caching layer for session tokens in a legacy microservice, reducing average auth latency by 100ms
  • Migrated legacy JavaScript utilities to TypeScript and improved CLI tooling serving 20K+ daily users
Project Tech stack:
Node.js
Typescript
Redis
Unit testing
CI
CD
React
Python
Java

Education

2025
Software Engineering
Bachelor's degree

Languages

Catalan
Upper-intermediate
Spanish
Advanced
Portuguese
Advanced
Korean
Intermediate
German
Intermediate
English
Advanced

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