Costa Rica · Available for remote

Sebastián Murillo

Computer Systems Engineer/security mindset, ships full-stack.

I think in systems and ship end-to-end. The browser is one of the layers I deliver — alongside OAuth flows, encrypted token storage and the Cloud Functions doing the actual work. I want the whole problem in front of me, not a single slice — the interesting engineering usually shows up in the seams between layers.

NOW today · sharpening TypeScript on PlaylistLab’s Cloud Functions, refreshing React, ramping on Adobe Experience Manager.

01

About

I’m a Computer Systems Engineer from Universidad Fidélitas. I build for the browser, but my foundation goes deeper — networking, Linux, security primitives, and a full-stack project I’ve shipped solo, end‑to‑end.

I’ve spent the last year in customer support. Tier 1 for Klaviyo at Concentrix (Aug 2025–Jan 2026) put me inside HTML/CSS email templates, browser DevTools and deliverability mechanics (SPF/DKIM) — reading and debugging other people’s markup under pressure, then explaining the fix in writing. After that, the Home Depot account at Movate (Feb–May 2026): real-time English support for US customers under SLA — daily practice writing clearly and thinking on my feet.

Right now I’m reactivating React intensively, deepening TypeScript and ramping on Adobe Experience Manager (HTL, Sling Models, JCR, Clientlibs) so I can contribute to enterprise component work — not just spec.

02

Systems & Security

Front-end is the surface. My foundation runs deeper — and it shapes how I think about OAuth, secrets, and what should never reach the browser.

Cisco Networking Academy: CCNA modules 1–2 (Introduction to Networks, SRWE) and Cisco IoT Fundamentals. TCP/IP, DNS, DHCP, VPN, VLAN at a working level. Wireshark for packet-level debugging, VirtualBox for throwaway labs.

Five years of freelance IT support (2020–2025) — OS installs, home networks, hardware, remote assistance. That’s where the Linux/Windows command-line muscle memory comes from.

  1. i. Linux Hardening Labs Bash · Ubuntu · Kali Two documented labs on system tuning & security configuration. Step-by-step walkthroughs of what changed and why — written so a teammate can reproduce them.
03

Selected Work

  1. PlaylistLab landing page — hero section with the value proposition and a sample playlist preview.
  2. PlaylistLab generate dashboard — musical profile analysis with mood tags, audio fingerprint and AI prompt input.
  3. PlaylistLab — screenshot 3 of 9.
  4. PlaylistLab — screenshot 4 of 9.
  5. PlaylistLab — screenshot 5 of 9.
  6. PlaylistLab — screenshot 6 of 9.
  7. PlaylistLab — screenshot 7 of 9.
  8. PlaylistLab — screenshot 8 of 9.
  9. PlaylistLab — screenshot 9 of 9.

1 / 9

Featured project · 2025–2026

PlaylistLab.

An architecture exercise in the shape of a music app. Three layered OAuth flows (Firebase Google + Spotify + YouTube), tokens encrypted at rest with AES-256-CBC, a Firestore the client cannot touch — every read and write mediated by Cloud Functions.

What users see: a SaaS that generates personalised playlists from a free-text AI prompt and transfers them between Spotify and YouTube Music. Built solo, end‑to‑end. Deployed, publicly accessible, actively developing.

Architecture
Backend-mediated: firestore.rules is deny-all; every read/write goes through the Admin SDK in Cloud Functions. OAuth tokens AES-256 encrypted before storage, decrypted server-side only.
OAuth
Three flows stacked: Firebase Google Sign-In (app identity) · Spotify (music data) · YouTube (cross-platform transfer). Callbacks route through dedicated paths (/callback, /youtube-callback).
Stack
React 19 + Vite (JS) on the frontend · TypeScript on Firebase Cloud Functions v2 (26 endpoints) · Firestore · Spotify, YouTube & Last.fm APIs · Groq · OAuth 2.0 · Lemon Squeezy
Role
Sole engineer · product, architecture, frontend, backend, deploy
Status
Deployed · publicly accessible · actively developing
Visit live site Source: private · actively developing
04

Skills

Systems & Security

Linux (Ubuntu, Kali), Windows 10/11, macOS. TCP/IP, DNS, DHCP, VPN, VLAN. Cisco Networking Academy — CCNA modules 1–2 & IoT Fundamentals. Wireshark, RDP, VirtualBox, Git/GitHub, ServiceNow, Zendesk.

Back-End & Data

Firebase Cloud Functions v2 (TypeScript), firebase-admin, Cloud Firestore, Firebase Auth, REST APIs, OAuth 2.0, JSON, Groq SDK, axios, Node.js. Python and Bash at a scripting level.

Front-End

HTML5, CSS3, JavaScript (ES6+), React 19, Vite, Tailwind CSS, react-router, react-i18next, Browser DevTools, cross-browser debugging, responsive web design (mobile‑first), accessibility (WCAG AA). Currently ramping: Adobe Experience Manager — HTL, Sling Models, JCR, Clientlibs.

05

Contact

Looking for a role where I can ship full-stack with care — front-end, back-end, security primitives, the whole thing. If that’s you, write me —