Sergio Valentin d.

Your site or system is slow, fragile, or held together by things nobody fully understands. I fix that with clean custom code: WordPress and WooCommerce sites that run for years, and full-stack software (Next.js, Node, Python) with the integrations and AI features that have to hold up in production. I've built on WordPress since v1.5 (2005) and shipped full-stack work for 18+ years: 13 years as founding developer at a US marketing agency (Loganix), where I built its custom theme, internal AI tools and BI dashboards. Then BI and integration work for a 3PL, a lead engineer role on an AI agent for a real-estate CRM, and today WooCommerce systems engineer for a US telehealth subscription platform. Results you can verify: 1. Telehealth WooCommerce platform: subscription renewals, failed-payment recovery, Stripe billing, and a custom plugin connecting the prescription platform to order flows 2. Law firm site: mobile PageSpeed 49 → 95, Total Blocking Time 1,160ms → 30ms 3. Capital partners site: PageSpeed 62 → 98, LCP 7.5s → 1.6s, CLS 0.112 → 0.001 4. CBD retailer: near-real-time WooCommerce stock sync with the in-store POS 5. AI agent for a real-estate CRM: every LLM call goes through one function, nothing the model writes reaches a client unless it traces to a real record, and every send needs a one-approval-one-send gate 6. 3PL BI platform: Next.js dashboard on BigQuery and Cloud Run over 2.26M invoice rows, demoed on dummy data in week one while access was sorted 7. Six MCP servers built, including natural-language SQL access to a live business database for an internal team, plus querychat, an open-source chat-your-database tool on my GitHub What I build for you: 🛒 WooCommerce: Subscriptions, custom checkout, renewal logic, Stripe, POS/shipping/ERP integrations 🧩 WordPress plugins and themes: OOP PHP 8, REST endpoints, webhooks, ACF, no page-builder lock-in ⚡ Speed & Core Web Vitals: LCP/TBT/CLS fixes, caching, MySQL query and index tuning 🛡️ Rescue & migration: hacked or broken sites, host moves, safe core and plugin updates 🧱 Web apps: Next.js, React, Node and TypeScript, Angular, PostgreSQL or MongoDB, Stripe billing, multi-role auth 🔌 Integrations: REST APIs, OAuth 2.0, webhooks with retries, refunds and idempotency handled, affiliate and referral tracking 📊 Data & BI: Python ETL, BigQuery, Cloud Run, dashboards on your real data 🤖 AI features: agents with guardrails, natural-language-to-SQL, MCP servers, AI search and chat inside your product or WordPress site How we'll work: 1. You send the brief → I reply with a written scope, risks, and a fixed price or estimate 2. All work happens on staging first, with a short bullet update at the end of every day in Upwork Messages 3. Tested, documented handoff. Code in your Git repo. You own everything. Bilingual (English/Spanish), working US time zones, open to long-term retainers. Tell me in 2-3 lines what you need built or what's broken and when you need it. I'll reply within a few hours with what I'd check first.