Computer Engineer · Senior Full Stack Developer

Juan
Llinares.

I build software people actually use. By day, software for tax administrations in Spain and Latin America at gtt; the rest of the time, my own products like Gym.y and Bruto, with one rule: easy to use and accessible to everyone.

Alicante, Spain
Open to freelance work and new opportunities
Bruto: #14 of the day on Product Hunt (opens in a new tab)

See my work Email me

Now buildingMore than a Hack Gym.y kawa-anatomy

01 / Barça

More than a Hack 2027 · Talent Arena, BarcelonaPhase 1 · in play

Who has the ball?

The football data hackathon by FC Barcelona, Metrica Sports and Mobile World Capital Barcelona. One full LaLiga match, Barça against Athletic Club, with automatic tracking of every player and the ball, and one question: which team has the ball, frame by frame. A script scores it against the real answer, with no jury.

I compete with GTT, a team of five. We study first, write down what we find and only then code, and every experiment goes in the log, failures included.
I built the team's website and its log. An entry can draw timelines and pitches whose scores come from a TypeScript port of the official metric, so no number is typed by hand.
I wrote the first studies: what the metric really rewards, and why tuning against the five public minutes would mislead us.

frames to label: 199,319
of the scored frames with the ball out of sight: 41%
baseline spellF1 to beat: 0.2433
people, one codebase: 5

20 Oct – 17 Nov 2026Now
Initial Challenge
The possession CSV, a public repository and a technical write-up.
All teams
26 Nov 2026 – 14 Jan 2027
Innovation Challenge
Open analytical and tactical questions on the same match.
Top 20
2 Mar 2027
Final Pitch
On stage at Talent Arena, in front of a professional jury.
Top 5

02 / Work

Selected work

Products I have designed, built and shipped. The first two are live and in use.

Three phones with Gym.y, each in a different theme color: today's workout from the routine, a set being logged in training mode, and the muscle map in Progress

2026In production

Gym.y (opens in a new tab)

A training log made to be used at the gym, with your phone in one hand. It started as my own and now also serves coaches and their athletes.

Distraction-free mode to log set by set, with RIR and rest timers.
Coach mode: plan mesocycles, assign routines and follow each athlete's progress. The athlete decides what to share.
Friends and share links for plans, routines and exercises, milestones across your whole history, and a character you design piece by piece.
Installable app with push notifications for rests, reminders and news from your coach.
Each user's data is isolated in Postgres with row-level security.

Next.js
TypeScript
Supabase
PostgreSQL
PWA
Web Push

Private code

Bruto board with notes connected by arrows, each with its age, and the note editor open

2026Finished · open source#14 of the day on Product Hunt

Bruto (opens in a new tab)

A brutalist, local-first task board for building projects with AI. It started as a tool for my own work at gtt and I use it every day: the notes live in a file inside each project, so you and any assistant work from the same source.

#14 of the day on Product Hunt (30 September 2026) among 1,134 launches, built by one person, with fixes from the comments shipped that same day.
Your AI assistant reads the notes and answers inside them, over MCP or with the context you copy with one key. You review and ask for changes in the note itself.
Every change an agent makes over MCP is on record: who made it, when and with what, tied to the commit and the exact files. A note can be read-only for agents. The MCP server is on npm as bruto-mcp.
It understands the project: web pages and components, APIs (.NET, Express, Spring…) and databases (Oracle PL/SQL, PostgreSQL, Prisma…). A note can block or relate to one on another project's board.
No account and no server: install it as an app, use it offline, in 9 languages.

React
TypeScript
Vite
File System Access API
MCP
Node.js
PWA
Playwright

Code @brutoboard Product Hunt

kawa-anatomy cover: the whole ZX-6R G in isometric drawing, the engine running inside out with its pistons, cam chain and oil, and the card of a part with its part number, torque and manual page

2026In development

kawa-anatomy (opens in a new tab)

My Kawasaki ZX-6R, piece by piece: interactive isometric drawings of every system on the bike, built from the factory service manual and the parts microfiche, plus a workshop logbook of what it needs and what has been done to it.

Twelve systems, each its own figure in the same world and camera: front brake, fork, cooling, engine, fuel, gearbox, chassis, wheels, exhaust, bodywork and electrics.
Every part carries its part number, how many the bike has, its tightening torque and the manual pages. The figures come apart in three stages and turn in 30° steps, each view with its own exact paint order.
They work live: the engine runs its four strokes, the coolant flows and the thermostat opens with temperature, the rear suspension compresses with the manual's progressive linkage, and the ignition key shows which wires conduct.
Curved bodywork drawn as surfaces sampled into isometric faces, with marching squares and light bands, something the drawing kit did not do.
Each page opens offline with no server; the logbook keeps the service history in Postgres on Neon.

JavaScript
SVG
Node.js
Anatomy kit
Neon
Vercel

Private code

2026In development

Homie

The whole home in one app, shared in real time: shopping, receipts, money, pantry, meals, chores, maintenance and documents. It reads receipts with its own OCR, warns before anything expires or renews, and the shopping list works with no signal. Self-hosted, with passkeys, and the data never goes through a third party.

React
TypeScript
Hono
SQLite
Drizzle
PWA
Docker

Private code

Beacon Split window with project tabs along the top, a Claude Code session on the left and the project's files and git changes on the right

2026Finished

Beacon Split (opens in a new tab)

Edu Ruiz's workspace for running several Claude Code sessions at once, each with real terminals, files and git, and a tab that says which one is waiting for an answer. I ported it to Windows (a new transport to its background daemon, Windows' pseudo-console and an installer) and kept building it with him until it was done.

Tauri
Rust
React
TypeScript
xterm.js

CodeWithEdu Ruiz

2026

nhoa (opens in a new tab)

Portfolio for Ainhoa Franco, who works in marketing, advertising and PR: editorial design, her work told as campaign case studies, and all the content editable from a single file.

Next.js
TypeScript
Tailwind CSS

Private code

More on GitHubExperiments, university assignments and small tools.

03 / Experience

Professional trajectory

Passionate about creating and inspired by what I have yet to master. Ignorance is just a state of transition.

Jul 2025 - Present
Work
Senior Full Stack Developer
gtt - Gestión Tributaria Territorial S.A.
I build software for tax administrations in Spain, Costa Rica, Honduras and Colombia. Every day I work across all three layers: the virtual office citizens use, the APIs behind it and the Oracle database.
- Pages of the virtual office that citizens use for their tax procedures, in Nuxt and Vue.
- Views of SIT, the tax management system civil servants work with every day, in its case files module.
- APIs in C# and .NET 10, WCF services, and Oracle tables and PL/SQL packages.
- Around 120 end-to-end tests with Playwright for Spain and Costa Rica, which also check the database and the PDFs the system generates.
2023 - 2025
Work
eduroam IT Support
University of Alicante
I helped students of the University of Alicante, and visitors from other universities, connect to eduroam. Real problems from real users: a lesson I apply to everything I build.
- Support on Windows, macOS, Linux, Android, iOS and Chromebook.
- Help in Spanish, Valencian and English.
- Problems solved on the spot.
2020 - 2025
Education
Degree in Computer Engineering
University of Alicante
Final degree project graded 9 out of 10: a machine learning model that predicts how resilient a program is to the errors radiation causes in hardware, learning from how the program runs.
- Dynamic traces of each program with LLVM-Tracer, turned into 30 features with PARIS.
- A fault injection campaign with UN-FIT to train and check the model.
- Read the thesis (opens in a new tab)
- Code (opens in a new tab)
The bit each injected fault flipsTubes, left to right: unACE, SDC and hangNeedle: what the model predicts. Mark: what UN-FIT measuredUN-FIT runs each program on an emulated Cortex-A15 and, at a random instruction, flips one bit of a register: 50 times per register, 3,000 per program. Each run ends fine (unACE), with a wrong result (SDC) or hung (hang). The model predicts unACE from 30 features of the dynamic trace, without injecting anything.

Tech I work with

Languages: TypeScript
JavaScript
C#
Java
C++
PL/SQL
Front end: React
Next.js
Vue
Nuxt
Tailwind CSS
Back end and data: .NET
Node.js
Supabase
PostgreSQL
Oracle
Testing and tools: Playwright
Vite
Git
Docker

Languages

Spanish: Native
Valencian: Native
English: B1 (Cambridge), comfortable working in it

Certifications · OpenWebinars

Generative AI and prompt engineering20263 courses
Oracle performance2025Analysis, tools, statistics and indexes · 3 courses
C#2025C# and intermediate C#
SQL and PL/SQL2025SQL, SQL Server and PL/SQL fundamentals
JavaScript and Git2025JavaScript fundamentals and Git

04 / Contact

Let's build something together.

Have a project in mind, or want to talk about one of mine? I take on freelance work and I'm open to new opportunities.

jllinaresjobs@gmail.com

JuanLlinares.

Who has the ball?

Initial Challenge

Innovation Challenge

Final Pitch

Selected work

Gym.y (opens in a new tab)

Bruto (opens in a new tab)

kawa-anatomy (opens in a new tab)

Homie

Beacon Split (opens in a new tab)

nhoa (opens in a new tab)

Professional trajectory

Senior Full Stack Developer

eduroam IT Support

Degree in Computer Engineering

Tech I work with

Languages

Certifications · OpenWebinars

Let's build something together.

Juan
Llinares.