Arnaud is available for hire
Hire ArnaudArnaud Mesureur
Verified Expert in Engineering
Ruby on Rails (RoR) Developer
Lisbon, Portugal
Toptal member since October 4, 2019
Bio
Arnaud has a proven track record of managing engineering teams and building scalable web applications in fast-paced environments. His experience ranges from building high-end web performance analytics platforms to being the head of engineering of a successful online marketplace. Arnaud recently led a project to design and build a payments platform that handles millions of transactions for one of the largest global micro-mobility operators.
Portfolio
FullScript - FSLV Holdings LLC
Ruby on Rails (RoR), JavaScript, SQL, API Management, Claude Code, Codex...
Healthcare Company
Python, JavaScript, PostgreSQL, FastAPI, Redis, OpenAI, Wellsky, AlayaCare...
Supportive, Inc.
PostgreSQL, Node.js, Ruby, Ruby on Rails 7, Ruby on Rails (RoR)...
Experience
- Full-stack - 10 years
- Solution Architecture - 10 years
- Ruby on Rails (RoR) - 10 years
- Databases - 8 years
- Technical Leadership - 8 years
- Python - 4 years
- AI Engineering - 3 years
- Large Language Models (LLMs) - 2 years
Work Experience
Senior Back-end Ruby Developer
2025 - PRESENT
FullScript - FSLV Holdings LLC
- Joined a newly formed team and shipped six projects into production in less than two months.
- Improved the event tracking of the labs customer and practitioner flow to enhance data-driven decision capabilities of the product team.
- Led projects from design to release as part of the labs team to enhance the customer experience of the healthcare platform.
Technologies: Ruby on Rails (RoR), JavaScript, SQL, API Management, Claude Code, Codex, Claude, Artificial Intelligence (AI), Full-stack Development, Software Engineering, AI-assisted Development, Web Application Architecture, APIs, Back-end, Back-end Development, HTML, Healthcare Software, HIPAA, REST, Integration, JSON, Third-party APIs, Enterprise Systems, Third-party Integration, Authentication, AI Security, Compliance, AI Compliance, Data Pipelines, AI Engineering, HIPAA Compliance, System Design, Cloud Infrastructure, Code Review
Lead Engineer
2026 - 2026
Healthcare Company
- Architected and shipped a staffing platform for home healthcare agencies, as the sole engineer. Including backend, frontend and a real-time voice agent.
- Built an AI outreach system that fills open shifts by phone and SMS, pairing LiveKit voice agents with a conversational SMS agent that parses partial availability into structured shift responses.
- Designed the platform's HIPAA compliance boundary so that no protected health information is stored at rest.
- Benchmarked a streaming STT/LLM/TTS pipeline against speech-to-speech, cutting projected inference cost 3.8x.
- Reverse-engineered and integrated two EHR systems with no usable public API.
Technologies: Python, JavaScript, PostgreSQL, FastAPI, Redis, OpenAI, Wellsky, AlayaCare, LiveKit, Telnyx, Deepgram, Cartesia, AI Agents, Artificial Intelligence (AI), Back-end, Back-end Development, HTML, Healthcare Software, HIPAA, Anthropic, Claude API, Agentic AI, Prompt Engineering, AI Agent Orchestration, Model Context Protocol (MCP), REST, Integration, JSON, Third-party APIs, Third-party Integration, Authentication, AI Security, Compliance, AI Compliance, Machine Learning, Retrieval-augmented Generation (RAG), System Integration, AI Engineering, Integrations, HIPAA Compliance, System Design, Cloud Infrastructure, Application Security, Code Review, Harness
Ruby/Ruby on Rails Back-end Engineer/Architect
2024 - 2025
Supportive, Inc.
- Designed and built an AI assistant application for nutrition tracking from the ground up based on OpenAI chat completion API.
- Built a suite of evals and a fine-tuning framework for the LLM prompts.
- Built various integrations for feeding context to the assistant, including Gmail and external nutritional databases.
Technologies: PostgreSQL, Node.js, Ruby, Ruby on Rails 7, Ruby on Rails (RoR), Scalable Web Services, Concurrency, REST APIs, GraphQL, Large Language Models (LLMs), TypeScript, Go, OpenAI, Anthropic, Artificial Intelligence (AI), iOS, LangChain, API Integration, API Management, Claude Code, Codex, Claude, Full-stack Development, Software Engineering, AI-assisted Development, Google Cloud, Web Application Architecture, AI Agents, AI Integration, APIs, Back-end, Back-end Development, HTML, Agentic AI, Prompt Engineering, AI Agent Orchestration, Model Context Protocol (MCP), REST, Integration, JSON, Third-party APIs, Third-party Integration, Authentication, AI Security, Machine Learning, Retrieval-augmented Generation (RAG), System Integration, AI Engineering, OAuth, Integrations, System Design, Cloud Infrastructure, Code Review, Harness, LangGraph
Staff Software Engineer
2020 - 2024
Spin
- Designed and implemented a service handling all tax submissions.
- Led the payment service team and supervised the design and implementation of a new payment service capable of supporting multiple payment providers side by side and handling payments across multiple merchants.
- Handled multiple PSP migrations, most notably from Stripe to Adyen.
- Designed and implemented payments via the PayPal feature.
Technologies: Ruby on Rails (RoR), Adyen Payments, Stripe Payments, Leadership, Agile Software Development, Web Architecture, API Architecture, Amazon Web Services (AWS), Object-oriented Programming (OOP), Sidekiq, Architecture, Online Payments, Databases, RSpec, Web Development, Solution Architecture, TypeScript, Node.js, React, SQL, Kubernetes, CI/CD Pipelines, Unit Testing, Integration Testing, Microservices, Microservices Architecture, Technical Architecture, API Development, Design Patterns, Software Architecture, Technical Leadership, Test-driven Development (TDD), Minimum Viable Product (MVP), Team Leadership, Next.js, Python 3, Apache Kafka, API Integration, API Management, Event-driven Design (EDD), Python, Full-stack Development, Software Engineering, Real-time Data, Telemetry, Web Application Architecture, APIs, Back-end, Back-end Development, REST, Integration, JSON, Third-party APIs, Enterprise Systems, Third-party Integration, Authentication, Single Sign-on (SSO), Data Pipelines, System Integration, Stripe, OAuth, Integrations, Enterprise Architecture, System Design, Service-oriented Architecture (SOA), Cloud Infrastructure, Application Security, Authorization, Code Review
Lead Software Engineer
2019 - 2020
Quinn
- Led the development of a payment, tipping, and vendor management system for an audio sharing platform using Ruby on Rails (RoR) and React.
- Migrated and scaled the entire infrastructure from DigitalOcean to Heroku.
- Implemented coding best practices and guidelines into the front-end React application and the Ruby on Rails codebase.
- Refactored the data modeling at the application and database level.
Technologies: PostgreSQL, React, Ruby on Rails (RoR), Ruby, Web Architecture, API Architecture, Object-oriented Programming (OOP), Architecture, Google Analytics, Online Payments, Databases, RSpec, Web Development, Node.js, SQL, GraphQL, CI/CD Pipelines, Unit Testing, Integration Testing, Technical Architecture, API Development, Design Patterns, Software Architecture, Full-stack, HTML5, Technical Leadership, Test-driven Development (TDD), Minimum Viable Product (MVP), Team Leadership, User Interface (UI), API Integration, Full-stack Development, Software Engineering, Web Application Architecture, APIs, Back-end, Back-end Development, HTML, REST, JSON, Third-party APIs, Third-party Integration, Authentication, Vercel, Single Sign-on (SSO), Stripe, OAuth, Integrations, System Design, Azure, Cloud Infrastructure, Authorization, Code Review
Head of Engineering
2015 - 2019
Flippa
- Shaped the business by participating in hiring, C-level meetings, business intelligence analytics, and reporting and leading the engineering and product team using Lean and Agile methodologies.
- Developed and maintained the core Ruby on Rails (RoR) marketplace, React front-end, and the AWS infrastructure.
- Implemented an event system with RabbitMQ to support interfacing the core Ruby on Rails application efficiently with multiple external services (SOA).
- Built and maintained advanced search features using Elasticsearch.
- Constructed a high-traffic name server for domain parking pages using Elixir.
- Implemented the funnel and conversion tracking with Google Analytics and Google Tag Manager.
Technologies: Amazon Web Services (AWS), Docker, Heroku, React, JavaScript, RabbitMQ, Redis, PostgreSQL, MySQL, Ruby on Rails (RoR), Ruby, Web Architecture, API Architecture, Amazon S3 (AWS S3), Business Strategy, Leadership, Object-oriented Programming (OOP), Sidekiq, Google Tag Manager, Stripe Payments, Architecture, Google Analytics, Online Payments, Databases, RSpec, Web Development, Solution Architecture, Node.js, SQL, GraphQL, Kubernetes, CI/CD Pipelines, Unit Testing, Integration Testing, Microservices, Microservices Architecture, Technical Architecture, API Development, Design Patterns, Software Architecture, Full-stack, HTML5, Technical Leadership, Test-driven Development (TDD), Minimum Viable Product (MVP), Team Leadership, User Interface (UI), API Integration, Event-driven Design (EDD), Python, Full-stack Development, Software Engineering, Real-time Data, Telemetry, Web Application Architecture, APIs, Back-end, Back-end Development, iOS, HTML, JSON, Enterprise Systems, Third-party Integration, Authentication, Single Sign-on (SSO), Machine Learning, Data Pipelines, System Integration, Stripe, OAuth, Integrations, Enterprise Architecture, System Design, Service-oriented Architecture (SOA), Cloud Infrastructure, Application Security, Authorization, Code Review
Senior Software Engineer
2015 - 2015
Washos
- Delivered a back-office interface for contractors of one of the first on-demand car-wash companies in the US.
- Implemented significant application and database optimization to improve the overall performance of the platform.
- Trained the engineering team on tooling, processes and best practices around web and database performance and performance regression testing.
Technologies: Ruby on Rails (RoR), Ruby, Web Architecture, Object-oriented Programming (OOP), Databases, RSpec, Web Development, SQL, Unit Testing, Integration Testing, Technical Architecture, Full-stack, Test-driven Development (TDD), Minimum Viable Product (MVP), User Interface (UI), Web Application Architecture, APIs, Back-end, Back-end Development, iOS, HTML
Senior Software Engineer
2015 - 2015
Mobile Network
- Designed, implemented, and delivered a business-critical platform for Apple device enrollment for a mobile device management (MDM) and enterprise mobility management (EMM) company.
- Implemented a search and bulk action interface that allowed tasks that would typically take a few days to be executed in a few minutes.
- Migrated the on-premise infrastructure to the cloud with the addition of a full test suite and a CI/CD pipeline, allowing for a drastically improved development experience and ease of maintainability.
Technologies: Apple, Heroku, Ruby on Rails (RoR), Ruby, Web Architecture, Object-oriented Programming (OOP), Databases, RSpec, Web Development, SQL, Unit Testing, Integration Testing, Technical Architecture, Full-stack, Minimum Viable Product (MVP), User Interface (UI), Tailwind CSS, API Integration, Web Application Architecture, APIs, Back-end, HTML
Software Engineer
2013 - 2014
Quanta
- Created the first proof of concept (POC) and minimum viable product (MVP) of the web performance monitoring platform for eCommerce websites.
- Developed and maintained the core SaaS solution with Ruby on Rails (RoR), MySQL, Redis, and AngularJS.
- Constructed a Google Analytics poller service to capture business intelligence (BI) data at regular intervals.
- Built a Zabbix poller service to capture host performance data at regular intervals.
- Developed a Magento poller service to capture application performance data at regular intervals.
Technologies: Sidekiq, Redis, MySQL, Ruby on Rails (RoR), Ruby, Web Architecture, API Architecture, Object-oriented Programming (OOP), Architecture, Databases, RSpec, Web Development, SQL, Unit Testing, Integration Testing, Technical Architecture, Full-stack, HTML5, Test-driven Development (TDD), Minimum Viable Product (MVP), Team Leadership, User Interface (UI), Data Visualization, Python 3, API Integration, Real-time Data, Telemetry, Web Application Architecture, APIs, Back-end, HTML, System Design
Experience
AI-powered Fitness and Nutrition Assistant
An iOS application for AI-assisted nutrition and fitness tracking. I designed and built the back end and infrastructure in direct collaboration with the founder and one mobile app developer. The development mostly focused on perfecting the results of the large language model (LLM) agents chain by working on a suite of evals and fine-tuning examples with custom built tooling to enable fast iteration and measurable improvements.
Payment Service for Micro-mobility Operator
A payment service for micro-mobility operators handling millions in transactions. Designed and built from the ground up. The service handles multiple payment providers, including Adyen and Stripe, side by side.
Flippa
https://www.flippa.comFlippa is the number-one marketplace to buy and sell online businesses. It's a one-of-a-kind business with technical and product challenges, mainly around trust, marketplace integrity, and verification. Millions of users registered, and hundreds of thousands of unique visitors come to the site each month.
Quanta
Quanta is a web performance analytics and monitoring SaaS platform for eCommerce websites. The application collects and processes gigantic amounts of data—billions of SQL rows generated and processed weekly, rendered within an intuitive, beautiful, and modern JavaScript standalone application. This project pushed the limits in terms of data storage and processing. It's not your average CRUD app!
Washos | On-demand Mobile Car Wash
https://www.washos.com/In the words of the founder and CTO, Benjamin Guez:
“Arnaud is a fast learner. He jumped in a massive Rails codebase at @washos and has immediately been involved in critical customer-facing features. His capacity to handle production apps with professionalism and tons of best practices impressed us. I would hire Arnaud without any question, from back end to front end with even knowledge in iOS, he's the full-stack engineer we all want in our teams."
“Arnaud is a fast learner. He jumped in a massive Rails codebase at @washos and has immediately been involved in critical customer-facing features. His capacity to handle production apps with professionalism and tons of best practices impressed us. I would hire Arnaud without any question, from back end to front end with even knowledge in iOS, he's the full-stack engineer we all want in our teams."
Education
2009 - 2014
Master's Degree in Computer Science
EPITECH (Ecole pour l'Informatique et les nouvelles Technologies) - Paris, France
2012 - 2013
Diploma in Intensive English
California State University, Long Beach - Long Beach, CA, USA
Skills
Libraries/APIs
React, Sidekiq, Stripe, Node.js, API Development, REST APIs, Claude API, Google Analytics API, OpenAI API
Tools
Git, Adyen Payments, RSpec, RabbitMQ, Google Analytics, Claude Code, Claude, Vim Text Editor, Codex, AlayaCare
Languages
Ruby, JavaScript, TypeScript, SQL, HTML5, Python, HTML, GraphQL, Python 3, C, Go
Frameworks
Ruby on Rails (RoR), Tailwind CSS, Next.js, LangGraph, Ruby on Rails 7
Paradigms
Web Architecture, API Architecture, Agile Software Development, Object-oriented Programming (OOP), Unit Testing, Microservices, Microservices Architecture, Design Patterns, Test-driven Development (TDD), Event-driven Design (EDD), Web Application Architecture, REST, Service-oriented Architecture (SOA), Model Context Protocol (MCP), HIPAA Compliance
Platforms
Docker, Amazon Web Services (AWS), Heroku, Mixpanel, Amazon EC2, Apache Kafka, Kubernetes, iOS, Vercel, Azure, Harness, MacOS, Apple, Algolia, Visual Studio Code (VS Code), LiveKit, Telnyx
Storage
MySQL, PostgreSQL, Redis, Databases, JSON, Data Pipelines, Google Cloud, Elasticsearch, Amazon S3 (AWS S3)
Other
Leadership, Architecture, Computer Science, Stripe Payments, Online Payments, Web Development, Solution Architecture, CI/CD Pipelines, Integration Testing, Technical Architecture, Software Architecture, Full-stack, Technical Leadership, Minimum Viable Product (MVP), Team Leadership, User Interface (UI), Large Language Models (LLMs), API Integration, API Management, Full-stack Development, Software Engineering, AI-assisted Development, APIs, FastAPI, Back-end, Back-end Development, Integration, Third-party APIs, Enterprise Systems, Third-party Integration, Authentication, Single Sign-on (SSO), Retrieval-augmented Generation (RAG), System Integration, AI Engineering, OAuth, Integrations, Enterprise Architecture, System Design, Cloud Infrastructure, Application Security, Authorization, Code Review, Google Tag Manager, Data Visualization, Anthropic, Artificial Intelligence (AI), LangChain, Real-time Data, Telemetry, AI Agents, AI Integration, Healthcare Software, HIPAA, Agentic AI, Prompt Engineering, AI Agent Orchestration, AI Security, Compliance, AI Compliance, Business Strategy, Jumio, English, PayPal, Scalable Web Services, Concurrency, OpenAI, Wellsky, Deepgram, Cartesia, Machine Learning
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