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Senior Software Engineer, Madrid

Willians Nieves

I build front ends people enjoy using, and lately I build the harnesses that keep AI agents honest. Half human, half machine, one stack.

Find me onLinkedInGitHub

AI-generated portrait of Willians Nieves
  • React
  • TypeScript
  • Claude Code
  • LangGraph

Two halves, one developer.

Based in
Madrid, Spain
Role
Senior Software Engineer
Experience
8+ years
Off the clock
Guitar, games, family

I am a front end developer who got curious about what happens when the machine does half the typing. Turns out someone still has to think.

I have spent 8+ years building interfaces with React, Node.js and TypeScript, and I still enjoy the whole JavaScript ecosystem: new tech, patterns and best practices, as long as the person on the other side of the screen ends up with something good to use.

These days a lot of my work is AI-driven: automation, testing harnesses, observability agents and the specs that keep them all pointed the same way. I also lead teams, design solutions and build tools that help engineers write better code, faster.

Off the clock I am a father, a passionate guitar player, and someone who plays video games and makes them too.

AI engineering

Where I spend most of my time now: telling agents what to do, clearly, and checking that they did it.

AI-generated portrait of Willians Nieves, machine half
The machine half
  1. Step 01

    Shape the context

    An agent is only as good as what it can see. I design the context, the harness and the loop around it, and map how the pieces connect.

    • Context engineering
    • Harness engineering
    • Loop engineering
    • Graph engineering
  2. Step 02

    Write the spec first

    Spec-driven development with OpenSpec: decide what to build before anything starts building. I have given tech talks on it at Glintt.

    • SDD with OpenSpec
    • Claude Code
    • Codex
    • JEV, a System 1 decision model
  3. Step 03

    Let the agents work

    At Glintt I built an AI testing harness, a Java BFF subagent and a LangChain and Grafana observability agent. Several agents, one orchestra.

    • Multi-agent orchestration
    • LangChain
    • LangGraph
    • LangSmith
    • Vector databases

The path so far

Nine stops, mostly in front of a browser.

  1. Glintt Global

    May 2025 to present

    Senior Software Engineer, Madrid (remote)

    • Working with Orange on internal platforms: key modules for Billing, Consents and Provisioning, while modernizing the architecture.
    • Pioneering AI-driven workflows and automation: an AI testing harness, a Java BFF subagent and a LangChain and Grafana AI observability agent.
    • Better observability across Grafana and Kubernetes, plus tech talks on Spec-Driven Development.

    Stack

    • TDD
    • AI
    • React
    • Claude Code
    • Google Cloud
    • Java
    • LangChain
    • Kubernetes
    • OpenCode
    • Spec-Driven Development
    • Astro

  2. EF

    Jul 2023 to Feb 2025

    Senior Software Engineer, Madrid

    • Modernized the booking system for Private and Group Lessons (scheduling, teacher search, calendar optimization) for millions of students worldwide.
    • Led the migration of core applications to a new UI system for B2C and B2B customers, including lesson progress tracking and the homepage.
    • Infrastructure and backend on the side: Terraform, BFF endpoints and feature-flag rollouts.

    Stack

    • Next 14
    • React 18
    • Tailwind 4
    • Storybook
    • Jest
    • React Testing Library
    • SWR
    • GitHub Actions
    • Terraform
    • pnpm workspaces
    • Turborepo
    • Playwright
    • Scrum
    • Kanban

  3. Cardo Health

    Sep 2022 to Apr 2023

    Software Engineer, Barcelona

    • Features for the patient (mobile) and clinician (desktop) platforms, with usability and accessibility in healthcare in mind.
    • Launched the MVP of the Cardo Health app for Prosperia, payment history included.

    Stack

    • Next 12
    • React 18
    • Tailwind 3
    • Storybook
    • Material UI
    • Native UI
    • React Native
    • Jest
    • React Testing Library
    • SWR
    • Node.js
    • Fastify
    • Strapi
    • Vite
    • GitHub Actions
    • Playwright

  4. Instaply

    Feb 2020 to Sep 2022

    Frontend Lead Engineer, Barcelona

    • Led the frontend team: new features and legacy modernization, a GraphQL server upgrade and new UI components.
    • Testing with Cypress, Jest and Selenium, payments inside conversations, an admin panel migrated to React and the Airbnb JavaScript style guide across projects.

    Stack

    • React 16
    • GraphQL
    • Express
    • MUI
    • Socket.io
    • Redux
    • Redux-Observable
    • Koa
    • CircleCI
    • Webpack
    • Selenium

  5. I-Surance GmbH

    Aug 2018 to Sep 2020

    Frontend Lead Developer, Barcelona

    Stack

    • React
    • Emotion
    • Styled Components
    • Webpack
    • Axios
    • Cypress
    • Bitbucket Pipelines
    • AWS S3
    • CloudFront
    • Route 53

Earlier

  • Interiorvista, Lead Frontend developer

    Mar 2017 to Jul 2018

  • Foticos, Frontend developer

    Apr 2016 to Mar 2017

  • Nyx, Frontend developer

    Sep 2015 to Jun 2016

  • Teravision, Node.js backend developer

    Jan 2015

The toolbox

No progress bars. I would rather show you the list than grade myself.

  • AI tools

    • Claude
    • Codex
    • Cursor
    • OpenCode
    • Ollama
    • DeepSeek
    • Kimi
    • GLM
    • Hermes
    • GPT
    • V0

  • Frameworks

    • Express
    • Next
    • Nest
    • Fastify
    • Astro
    • FastAPI
    • Svelte
    • Vue
    • Angular
    • React Native

  • Frontend

    • HTML
    • CSS
    • TypeScript
    • JavaScript
    • React
    • Redux
    • GraphQL
    • RxJS
    • Tailwind
    • Playwright
    • Jest
    • React Testing Library
    • SWR
    • React Query

  • Principles

    • SOLID
    • CQS
    • DRY
    • Clean Architecture
    • POLA
    • YAGNI
    • Hexagonal

  • Workflow

    • GitHub
    • Bitbucket
    • Jira
    • Scrum
    • GitHub Actions
    • CircleCI
    • Vercel
    • Netlify
    • AWS
    • Terraform
    • Google Cloud
    • Kubernetes
    • Grafana

  • Soft skills

    • Perseverance
    • Continuous improvement
    • Collaboration in cross-functional teams
    • Communication with developers, product managers and stakeholders
    • Proactive problem solving

Beyond the code

The human half.

  • Dad

    The most demanding stakeholders live at home, and their roadmap changes every day.

  • Guitar

    A passionate player. It is the one place where I am happy to have no autocomplete.

  • Games

    I play video games and I make them. Debugging is more fun when the bug has a boss fight.

Education and languages

Education

Informatic engineering

Alejandro de Humboldt University, Caracas, Venezuela

2008 to 2011

Languages

  • SpanishNative
  • EnglishB2, improving towards C1