About

I build software and show my work.

Sebastian Castano Jara · Senior Software Engineer · Cali, Colombia

Portrait of Sebastian Castano Jara
Based in
Cali, Colombia (GMT-5)
Shipping since
2016
Role
Senior FullStack Engineer
Languages
Spanish (native) · English (C2)
Focus
AI-assisted development

My first paid code shipped in 2016, at a small software studio in Cali, straight out of a game development program at SENA. Learning to program by making games left me with a conviction I never dropped: software people enjoy using is a feature, not a luxury.

Since then I've spent eight-plus years shipping for companies across the Americas. Real-time transaction services, group video calls, dashboards with drag-and-drop, delivery platforms. I went from engineer to senior in under two years at a consulting firm, and today I ship products for international clients as a Senior FullStack Engineer.

I got AI wrong before I got it right.

I treated it like a faster autocomplete: vague prompt in, patch out, repeat. One session, a careless git stash ate eight of the ten files I'd been working on, and I rebuilt them from memory. That week pushed me to specs, tests, and git worktrees — a workflow where the model understands the project before writing a line. The whole story is in AI Gave Me Speed. Tests Gave Me Control.

This site is where I show that work. Every diagram in the posts is a live component you can poke (there are 30-plus of them in the lab), the todo app I plan my days with is mine, and the workflow the blog describes is the same one this site is built with.

Now

Updated June 2026
  • Finished my B.Eng. in Systems Engineering and the Claude Certified Architect exam, both this year.
  • Building todo.valdemird.com — AI scheduling, Pomodoro, drag-and-drop.
  • Exploring on-device AI in the browser. If your Chrome supports it, the chat button in the corner runs locally on your machine.
  • Writing about interactive components and running Claude agents in parallel.

What I work with

Frontend

ReactNext.jsAstroTypeScriptCSS/Design Systems

Backend

Node.jsPostgreSQLPrismaREST APIs

DevOps & Cloud

AWS (Certified)CI/CDDockerGitHub Actions

AI & Tooling

LLM IntegrationVercel AI SDKSpec-Driven DevelopmentCustom CLI Workflows

Journey

2022–Now

Senior FullStack Engineer · Nearshore Tech Company

Products for international clients: React, Next.js, cloud infrastructure.

2020–2022

Software Engineer → Senior · Software Consulting Firm

Engineer to senior in under two years, across several client projects.

2019–2020

Software Developer · Dev Agency

Real-time transactional services, group video calls, PDF report generators.

2017–2018

Freelance Engineer · Independent

Android apps, Arduino IoT integrations, Firebase backends.

2016–2017

Junior Developer · Software Studio

First professional role. Where it all started.

What I believe in

Spec-driven development

Write the spec before the code. Let the LLM be your co-architect, not just your typist.

I wrote about this →

Build in public

Share what you learn. The best way to solidify knowledge is to teach it.

I wrote about this →

Beauty & function

Tools should be beautiful and functional. Design is part of the message, not a coat of paint.

I wrote about this →

Background & credentials

Credential

Claude Certified Architect – Foundations Certification

Anthropic Education · Issued June 5, 2026

Anthropic's formal certification on architecting with Claude. The exam version of what the posts here document in practice: specs, agents, and tooling.

Verify credential →
2023 AWS Certified Cloud Practitioner
2020 EF SET English C2 Proficient
2020 Learning How to Learn, Coursera
2026 B.Eng. Systems Engineering, Universidad del Valle
2018 Technology Degree in Information Systems, Universidad del Valle
2016 Technology Degree in Game Development, SENA

Get in touch

I live in Cali, Colombia. Outside client work I build small multiplayer games at games.valdemird.com and tweak this site's components more than I should. If you want to talk shop, the form above or any of these works.