Léo Bello

React and Next.js application development

Designing and building React / Next.js interfaces in TypeScript: component architecture, state management, complex forms, server-side rendering.

API and AI integration

Wiring REST APIs, Node.js back-ends and AI services into an existing product, with real attention to loading states, failure paths and the actual cost of each call.

Rescuing and stabilising an existing front-end

Auditing a codebase, reworking its architecture, adding unit and component tests, paying down technical debt without freezing delivery.

Back-end and data

Node.js APIs, PostgreSQL / Supabase models, Firebase Firestore: from data modelling through to what the interface finally shows.

Web performance and quality

Measuring and improving Core Web Vitals, setting up automated tests and CI/CD pipelines that check every release.

Prospeo — End-to-end automated prospecting

Personal project · 2026

Thousands of tradespeople and small businesses have no website at all, and approaching them one by one costs more than it brings in. Prospeo automates the whole chain: it finds those businesses, builds them a site, puts it online, then sends them a proposal pointing at their own site — already live.

Detection through Google Maps, matching against the SIRENE company registry, and scoring that can be replayed on data already collected — criteria can be refined without crawling again. Copy written by an LLM under a strict schema, automatic Git commit and deployment, every step traced and timestamped. Human review before sending, email and SMS, with a database guarantee that a prospect can never be contacted twice.

A long, asynchronous, failure-prone business chain held together end to end: background job orchestration, three third-party APIs, AI-generated content constrained by a schema and therefore verifiable, multi-tenant isolation through RLS and encrypted secrets. 52,000 lines, 115 test files.

Technologies : React, Vite, PostgreSQL, RLS, LLM, Zod, Astro, Vercel, GitHub App, pnpm monorepo.

SignFlow — Job-listing watch, sorted by AI

Personal project · 2026

Looking for a role means re-reading the same listings across four sites that don't talk to each other, to keep three of them. SignFlow does that re-reading at night: four sources merged, republications of the same offer collapsed into a single entry, and one brief waiting in the morning.

Every offer is read by AI and checked against real criteria — remote work, pay, engagement length, technologies you no longer want to touch. Each ranking comes with its reason, and changing a criterion re-ranks the whole history instantly: the judgement is recomputed, not frozen at collection time.

Turning a raw feed into a decision: normalising heterogeneous sources, reliable deduplication, AI judgement that is reproducible and auditable, and a data model that accepts rule changes after the fact. Nothing is sent without approval — the product prepares the decision, it does not take it.

Technologies : React, Next.js, TypeScript, PostgreSQL, LLM, Structured output, Scheduled jobs, Real time.

Full-Stack Developer React / Next.js — built from scratch, freelance — Saisoneo

February 2026 — Present · Marseille · Remote

A seasonal rental management application built from scratch, from requirements gathering to production: technical architecture and data model defined from zero, with no existing codebase to inherit.

Fully developed with TDD — React / TypeScript front-end, Next.js back-end on Supabase and PostgreSQL — on a microservices, event-driven architecture designed to scale. Third-party integrations with SharePoint and Yousign, OAuth 2.0 / SSO authentication with full token lifecycle management.

A scope owned end to end rather than a single brick handed over: UX/UI mockups, tests written before the code, technical documentation, and deployment through CI/CD pipelines.

React, Next.js, TypeScript, Supabase, PostgreSQL, TDD, Microservices, Event-Driven, OAuth 2.0, SSO, CI/CD

Front-end Developer React / TypeScript — projects delivered end to end, freelance — Bleu Tomate

May 2025 — August 2026 · Marseille, Provence-Alpes-Côte d'Azur, France

Several communication campaigns carried end to end, from gathering the requirement to going live, as the sole technical contact on each project.

Scoping and technical architecture, interface mockups, then development: React / TypeScript front-end, API integration, Google Apps Script scripts and Cloud Functions on Firebase.

Shipping and follow-up count as much as the code: CI/CD pipelines, unit tests, technical documentation, and reading the KPIs once the project is in production.

React, TypeScript, REST API, Firebase, Cloud Functions, Google Apps Script, CI/CD

Full-Stack Developer React / TypeScript — high-volume application, permanent contract — Française des Jeux / Sopra Steria

November 2023 — April 2025 · Aix-en-Provence, Provence-Alpes-Côte d'Azur, France

A sales performance dashboard for La Française des Jeux: the performance metrics of nearly 29,000 points of sale across France, served continuously to field teams.

Complex features in React, TypeScript, and Redux Toolkit over large data volumes, within a five-person Agile team — two developers, a tech lead, a QA — running SAFe, with PI Plannings alongside design and the Product Manager.

Over eighteen months, quality was a production constraint rather than an intention: test coverage held around 80% (Jest, React Testing Library), code reviews, cross-testing between developers, and feature estimation.

React, TypeScript, Redux Toolkit, Jest, React Testing Library, SAFe, Agile

Web Developer React / TypeScript — e-commerce & ticketing, freelance — E-commerce & event ticketing client

May 2023 — October 2023 · Marseille, Provence-Alpes-Côte d'Azur, France

E-commerce sites and ticketing modules delivered in complete autonomy, from scoping the requirement and estimating it through to development and delivery.

Ticketing modules for the events industry, with validation and checking of order data; bespoke WordPress modules and Google Sheets scripts (Apps Script) automating recurring business tasks.

React, TypeScript, REST API, WordPress, Automation

Full-Stack Developer React / Node.js — international SaaS platform, freelance — Yooz

May 2022 — May 2023 · Aimargues, Occitanie, France

A SaaS platform for digitising and automating supplier invoices, used in more than 50 countries, from startups to large accounts.

Document approval workflows with dense business logic — multi-criteria approval chains, routing rules, edge cases — built in React, TypeScript, and Node.js, with REST APIs backed by PostgreSQL.

Working directly with the product team on software already running in customers' production: estimating requests, unit tests, and technical documentation.

React, TypeScript, Node.js, REST API, PostgreSQL, SaaS

Full-Stack Developer React / Node.js — integration & shipping, freelance — E-commerce clients — direct engagements

October 2021 — May 2022 · Remote

Websites shipped to production for e-commerce clients, from mockup to going live.

React, TypeScript, and Node.js engagements: integrating mockups, adding e-commerce modules and ticketing blocks to existing sites, and contributing to the design and delivery of a POC.

React, TypeScript, Node.js, REST API, Figma, JavaScript

Full-Stack Developer React / Java EE — apprenticeship — Amiltone

September 2020 — September 2021 · Villeurbanne, Auvergne-Rhône-Alpes, France

Maintenance and evolution of a business application already in production, on a stack combining React and Java EE.

Building change requests, fixing bugs, reviewing code, and writing technical documentation.

React, Java EE, REST API, Maintenance

Full-Stack Developer Angular / Java EE — Sully Group

September 2019 — July 2020 · Grenoble, Auvergne-Rhône-Alpes, France

Front-end and back-end development across several application layers, from estimation through to deployment.

Estimating requests, functional evolutions, regular code reviews, and writing user and technical documentation.

Angular, Java EE, HTML5, CSS3, Estimation

Web Development Intern — Sully Group

June 2019 — September 2019 · Grenoble, Auvergne-Rhône-Alpes, France

Delivered development requests and participated in code reviews. Technology monitoring, skill-building on project tools, and self-training on required topics.

Web Development, Technology Watch

Research Intern in Computer Science — computer vision and robotics — Grenoble Computer Science Laboratory (LIG)

May 2018 — August 2018 · Grenoble, Auvergne-Rhône-Alpes, France

A research topic at the intersection of machine learning and robotics: giving a Pepper robot the ability to recognise what it sees.

Building and training a convolutional neural network with PyTorch, then integrating the model into the robot.

Writing a wiki for the researchers, so the work stayed picked-up-able after the intern left.

Machine Learning, Deep Learning, PyTorch, Robotics

Who is Léo Bello?

Léo Bello is a freelance full-stack web developer based in Marseille, France, working with React, Next.js, TypeScript, PostgreSQL. Full-stack developer, seven years spent on applications that are not allowed to break: sales performance tracking across 29,000 points of sale for La Française des Jeux, an invoicing SaaS used in more than fifty countries, a rental management application written from scratch in TDD. I take a product from the interface down to the database, or I pick up an existing one — its debt, its overdue upgrades, its slowness — and ship it tested, documented, and ready for the next developer to take over.

Which technologies does Léo Bello work with?

Front-end: React, Next.js, TypeScript, JavaScript, Redux Toolkit, Tailwind CSS, Angular, Component Architecture, React Testing Library, Jest, Vitest. Back-end: Node.js, REST API, PostgreSQL, Supabase, Firebase Firestore, Java EE, Data Modelling, Authentication and Roles, Google Cloud Functions. Cloud and DevOps: Vercel, Firebase, Google Cloud, Cloud Computing, CI/CD, GitHub Actions, GitLab CI, pnpm Monorepo. Data and AI: LLM API Integration, OpenAI, Claude, Tool-Calling Agents, MCP, Machine Learning, Deep Learning, PyTorch, Neural Networks, Robotics. Tools and methods: Git, TDD, Code Review, Playwright, Agile / SAFe, Estimation, Technical Documentation, SEO, AI-Assisted Development, WordPress, Google Apps Script, Google Analytics. Soft skills: Autonomy, Requirements Framing, Rigor, Sole Technical Contact, Self-Learning, Technology Watch, Entrepreneurship, Cross-team Collaboration, Professional English.

Is Léo Bello available for freelance work?

Yes. Léo Bello takes on front-end and full-stack freelance engagements, from Marseille, France and remotely. The freelance profile, with rates and client recommendations, is published on Malt: https://www.malt.fr/profile/leobwebdev

How can I contact Léo Bello?

By email at leobello.wd@gmail.com, through the Malt profile (https://www.malt.fr/profile/leobwebdev), on LinkedIn (https://www.linkedin.com/in/leobellolinkedurl) or on GitHub (https://github.com/leoBello/). The portfolio is online at https://leobello.dev.

What is Léo Bello working on right now?

Full-Stack Developer React / Next.js — built from scratch, freelance at Saisoneo (February 2026 — Present, Marseille · Remote). A seasonal rental management application built from scratch, from requirements gathering to production: technical architecture and data model defined from zero, with no existing codebase to inherit. Fully developed with TDD — React / TypeScript front-end, Next.js back-end on Supabase and PostgreSQL — on a microservices, event-driven architecture designed to scale. Third-party integrations with SharePoint and Yousign, OAuth 2.0 / SSO authentication with full token lifecycle management. A scope owned end to end rather than a single brick handed over: UX/UI mockups, tests written before the code, technical documentation, and deployment through CI/CD pipelines.

What services does Léo Bello offer?

React and Next.js application development; API and AI integration; Rescuing and stabilising an existing front-end; Back-end and data; Web performance and quality.

Which personal projects has Léo Bello built?

Prospeo (End-to-end automated prospecting, 2026): Thousands of tradespeople and small businesses have no website at all, and approaching them one by one costs more than it brings in. Prospeo automates the whole chain: it finds those businesses, builds them a site, puts it online, then sends them a proposal pointing at their own site — already live. Technologies: React, Vite, PostgreSQL, RLS, LLM, Zod, Astro, Vercel, GitHub App, pnpm monorepo. SignFlow (Job-listing watch, sorted by AI, 2026): Looking for a role means re-reading the same listings across four sites that don't talk to each other, to keep three of them. SignFlow does that re-reading at night: four sources merged, republications of the same offer collapsed into a single entry, and one brief waiting in the morning. Technologies: React, Next.js, TypeScript, PostgreSQL, LLM, Structured output, Scheduled jobs, Real time.

What is the leobello.dev portfolio?

An interactive portfolio: a small 3D world to explore in the browser, built with React, TypeScript and Three.js (React Three Fiber), with Rapier physics. Five monuments open the five portfolio sections — about, skills, background, projects and contact. https://leobello.dev/en/profile/ is the text version.