Apr 2023 – Aug 2023 · Freelance · Remote
A web platform for hiring services: people publish the services they offer, and other users find and hire them.
The real-time chat with Socket.io was the biggest technical challenge of the project.
Frontend Developer · JavaScript · React · Next.js · React Native
This portfolio is designed as a code editor 💻. For the best experience, open it on a desktop browser.
Frontend Developer with 5+ years of experience building web and mobile applications for companies in Spain and Argentina, from the first design to production. I'm also Systems Manager at ST Group, which gives me an end-to-end view of product, business, and infrastructure.
summary.md: my whole profile on one page (ideal if you're short on time)experience/: where I've worked and what I've builtskills/: my stackprojects/: projects (starting with this portfolio)about/: education, certifications, languages and hobbiescontact/: let's talkcv/: download my resumeJavaScript · React · Next.js · React Native · Node.js · Tailwind CSS · Supabase
tvallejossemino@gmail.com · LinkedIn · GitHub
💡 Tip: open the terminal with Alt+T and type
help.
I'm a Frontend Developer with 5+ years of experience building web and mobile apps with JavaScript, React, Next.js, and React Native for companies in Spain and Argentina, from the first design to production.
Since 2026 I've also been Systems Manager at ST Group, leading infrastructure, cybersecurity, and custom software for 5 corporate clients. This gives me a close view of how technology impacts the business.
Clean, maintainable code, a strong focus on UX, ownership from idea to deployment, and clear communication.
15 Feb 2026 · Valid until 15 Feb 2028 · ID 5581514127TV
Earned during the 1st year of the B.S. in Cybersecurity (UNSO).
View certificate: certificates/fortinet-certified-fundamentals-cybersecurity.pdf · Verify
15 Feb 2026
Fortinet course, taken in Spanish.
View certificate: certificates/fortinet-introduction-to-the-threat-landscape.pdf
2 Feb 2026
Fortinet course, taken in Spanish.
View certificate: certificates/fortinet-getting-started-in-cybersecurity.pdf
Aug 2021 · ID EM866280
View certificate: certificates/plataforma5-full-stack-bootcamp.pdf
2021
View certificate: certificates/plataforma5-intro-frontend.pdf
Universidad Nacional Raúl Scalabrini Ortiz (UNSO)
In progress · 2nd year
As part of the first year I earned the Fortinet Certified Fundamentals in Cybersecurity certification (valid until 2028), along with the Getting Started in Cybersecurity and Introduction to the Threat Landscape courses. Details in about/certifications.md.
Plataforma 5 · Coding Bootcamp
Mar 2021 – Aug 2021
Intensive full-stack JavaScript program, completed after the Front End Introductory Module. The certificates are in certificates/.
Besides writing code, I make coffee: I'm a certified barista. I took the Barista & Latte Art Course at Puro Lab · Escuela de Baristas (March 2026, 2 months; certificate issued together with Escuela Gourmet Online and Puro Café).
That's why this portfolio's package.json starts with "dev": "coffee && code". Try typing coffee in the terminal.
Certificate: certificates/puro-lab-barista-latte-art.jpg
{"spanish": "Native","english": "Upper-intermediate (B2)"}
export const contact = {email: "tvallejossemino@gmail.com",linkedin: "linkedin.com/in/tomasvallejos",github: "github.com/Tvallejoss",location: "Buenos Aires, Argentina",status: "Open to work · Frontend / React Developer",};
Jan 2026 – Present · Buenos Aires
ST Group is an IT consulting firm. I run the systems area for 5 of its corporate clients, including +Vida and Román Servicios: from infrastructure and security to custom software, working alongside the CEOs and managers and leading the helpdesk technicians.
The Jira work at +Vida: process automation and metrics for several areas, plus custom apps built on top of the Jira API. One of the biggest achievements of this role so far.
Sep 2024 – Present · Freelance
A production mobile app, built from scratch for the bus drivers of the Flechabus group, a group of long-distance bus companies. It replaced the paper list drivers used to check who could board with a digital flow that works offline. The MVP reached production in 3 months.
Buses travel through areas with no signal, so the app is offline-first: it validates passengers and records each stop without internet, keeping that data in AsyncStorage. The hardest part was synchronization: making sure no record was ever lost when the connection came back mid-route, so Flechabus servers always end up knowing which passengers boarded at each stop.
Published on Android and iOS for internal use by the Flechabus group.
Jul 2023 – Present · Freelance
Buspack is the parcel and logistics company of the Flechabus group. I support and evolve its main application, where orders and customers are managed, and I built additional tools around it.
Fixing bugs in a legacy codebase while migrating React class components to modern React with hooks, and bringing outdated dependencies up to date without breaking production.
Aug 2023 – Sep 2026 · Full-time · Remote, Spain (Cantabria)
Hetmo builds software to quote any kind of window or door, used by clients across Europe and Latin America, including Obramat. I worked as a frontend developer on its main application and on metrics apps for the factories that manufacture those windows.
Spanish software company with 25+ years in management software and machinery integration for aluminium, PVC and wood joinery manufacturers, present in Spain, Portugal and Latin America.
Apr 2023 – Aug 2023 · Freelance · Remote
A web platform for hiring services: people publish the services they offer, and other users find and hire them.
The real-time chat with Socket.io was the biggest technical challenge of the project.
May 2022 – Apr 2023 · Freelance · Remote
A client project integrated with the NOBILIS clinical laboratory, which provided the test results. A web platform built so that a company can manage the medical tests of its employees in one place, designed as a product to sell to corporate clients.
Aug 2021 – Apr 2022 · Full-time · Remote, Argentina
My first role as a developer. NetGlobal builds a CRM, and DirecTV was one of its main clients.
Software development company with 20+ years building business-process solutions for the insurance, manufacturing and services industries.
My portfolio as a VS Code workspace: folders, tabs, a terminal, git history and skills as extensions.
The idea started in September 2022, in my first months as a developer: a React mock-up of the editor window. It stayed at that, a static mock-up.
In 2026 I picked it up again with four more years of experience and turned it into a complete application where every part of the interface actually works.
🔗 Source code · First sketch (2022)
/content. Each role generates its .md file, its Source Control commit and its terminal output, with no duplicated copy.Design inspired by VS Code (not affiliated with Microsoft).
export const backend = {runtime: ["Node.js"],frameworks: ["Express", "NestJS"],apis: ["REST APIs"],realtime: ["Socket.io"],};
{"baas": ["Supabase", "Firebase"],"sql": ["PostgreSQL", "MySQL"],"nosql": ["MongoDB"]}
version_control:- Git- GitHubcontainers:- Dockerdeploy:- Vercel- AWS- Heroku- Railway
export const frontend = {languages: ["JavaScript", "TypeScript", "HTML5", "CSS3", "Sass"],frameworks: ["React", "Next.js"],state: ["Redux"],styling: ["Tailwind CSS", "Material UI", "CSS Modules"],testing: ["Jest", "React Testing Library"],};
export const mobile = {frameworks: ["React Native"],tooling: ["Expo", "Expo EAS"],};
{"design": ["Figma", "v0"],"management": ["Jira", "Notion", "Scrum"],"ai": ["Claude Code", "Cursor", "ChatGPT"]}
# Things that never reach productionnode_modules/.env.env.local# Habits I left behindconsole.log("here")console.log("here 2")
{"name": "tvallejoss","version": "5.0.0","description": "Frontend Developer · 5+ years","author": "Tomás Vallejos Semino","scripts": {"dev": "coffee && code","hire": "mailto:tvallejossemino@gmail.com"},"dependencies": {"javascript": "^ES2026","react": "^19.2","next": "^16","react-native": "^0.8x","tailwindcss": "^4","node": "^24","supabase": "latest"}}
The whole profile on one page. 5+ years building web and mobile apps for companies in Spain and Argentina, from the first design to production.
Open to work: Frontend / React Developer, remote or hybrid.
Systems Manager · ST Group · Jan 2026 – Present
Frontend & Mobile Developer · Flechabus · Sep 2024 – Present
Frontend Developer · Buspack · Jul 2023 – Present
Frontend Developer · Hetmo Informática · Aug 2023 – Sep 2026
Frontend Developer · Vidual · Apr 2023 – Aug 2023
Frontend Developer · Laboratorio Córdoba · May 2022 – Apr 2023
Frontend Developer · NetGlobal Solutions · Aug 2021 – Apr 2022
☕ Certified barista: Barista & Latte Art Course (Puro Lab · Escuela de Baristas, Mar 2026)
Spanish (native) · English (upper-intermediate, B2)
/*** 👋 Hi! I'm Tomás.* This is my portfolio, built as a VS Code workspace:* you can browse my career as if you were exploring a repository.*/const name = "Tomás Vallejos Semino";const developer = {name,role: "Frontend Developer",stack: ["JavaScript", "React", "Next.js", "React Native"],experience: "5+ years",location: "Buenos Aires, Argentina",openToWork: true,};// 🧭 How to get around:// 📁 Browse the folders on the left: experience/, skills/, about/// 📄 .md files open as rendered documents, just like in VS Code// ⌨️ Ctrl+K finds files · F1 shows all commands// 💻 Alt+T opens the terminal: try typing "help"// 📬 Let's talk: contact/contact.js, or grab my resume in cv/export default developer;