Marc – React, Typescript, Node.js

A dermocosmetics company specializing in skincare, sun protection, and dermatological solutions. The project focused on supporting product's digital and technology ecosystem through backend development and cloud-based services. This included building and maintaining microservices, deploying and operating production systems, and developing AWS-based serverless components to ensure scalable, reliable, and efficient platform performance across business applications.

• Development and maintenance of microservices-based architecture
• Deployment and release management in production environments
• Development of AWS Lambda functions and serverless components, SQS, SNS, S3 buckets and more
• Management and support of AWS cloud infrastructure
• Participation in system reliability, scalability, and operational monitoring

It's an app that teaches you to speak English by having voice message conversations with chatbots in various common situations.

• Developed the entire product stack end-to-end, from back-end services to real-time front-end interfaces, owning all architectural decisions.
• Designed and implemented the payment and subscription infrastructure: full billing lifecycle (trials, renewals, upgrades, cancellations), webhook-driven processing of payment events with deduplication and retry handling, and synchronization of subscription state between payment providers and the internal database.
• Ensured transaction integrity for entitlement changes using atomic PostgreSQL operations, keeping user access consistent with billing state even under out-of-order or duplicate payment events.
• Built failed-payment recovery flows (grace periods, retry logic) to reduce involuntary churn.
• Implemented Generative AI & Speech Intelligence for natural, engaging conversations, integrating LLMs and Speech-to-Text for accurate, AI-driven language interactions.
• Built real-time conversation analysis systems (WebRTC, WebSockets) to provide actionable coaching feedback.
• Ensured privacy, security, and responsible AI practices — secure credential management, least-privilege access, and compliant handling of user data.

It's a known Spanish real estate company.

• Designed, developed, and maintained front-end and back-end applications supporting the company’s core business operations.
• Contributed to the migration and refactoring of legacy systems into modern, maintainable, and scalable architectures.
• Built and enhanced internal platforms that improve customer experience and operational efficiency across multiple business areas.
• Implemented data integrations, APIs, and analytics-ready solutions to support reporting and informed decision-making.
• Collaborated on building secure, reliable, and scalable systems capable of supporting national and international growth.
• Worked closely with engineers, product managers, and other stakeholders to deliver high-quality solutions and ensure technical alignment.

It's a platform that creates, experiments with, and optimizes online campaigns to help companies and brands grow, resulting in more visitors, high-quality leads, and strong revenue.

• Built and maintained both front-end and back-end systems, ensuring seamless functionality and user experience.
• Collaborated on designing scalable and robust systems aligned with the company’s product vision.
• Worked closely with cross-functional teams during sprint planning, code reviews, and release cycles to deliver high-quality products on time.

Worked as a freelance engineer on 20+ projects, primarily with early-stage startups, helping founders turn ideas into reliable, production-ready products.

• Built full-stack web applications from scratch (back-end services, front-end interfaces, APIs).
• Designed scalable system architectures suited for fast-growing startups.
• Developed real-time features such as chat, live updates, and interactive user experiences.
• Turned early concepts and rough requirements into working products and MVPs.
• Improved performance, stability, and maintainability in existing codebases.
• Worked directly with founders and small teams to align technical decisions with business goals.
• Implemented security, privacy, and best engineering practices in production environments.

An early-stage startup building a futures trading platform where users deposited real funds, tracked live market prices, and executed trades. Built the platform's financial backend and real-time trading interface, with a strong focus on transaction integrity, security, and reliability of money movement.

• Designed and built the core financial backend: user balances backed by a transactional ledger, deposits via card, bank transfer, and PayPal, and a withdrawal (payout) flow with full transaction history.
• Implemented order execution for futures trades with idempotency safeguards to prevent duplicate orders, and atomic PostgreSQL transactions coupling balance updates with order records.
• Built reliable webhook processing for payment and market-data events, with deduplication to guarantee exactly-once handling of external events.
• Developed a reconciliation process comparing internal records against external providers to detect and surface discrepancies.
• Integrated third-party market data feeds and built WebSocket-based real-time price streaming for futures instruments, with validation and fallback handling for degraded or malformed feed data.
• Built the React frontend: live price views, order placement, balance and transaction history.