Carlos OrtizSenior Full Stack Engineer

Founded and built ReactChallenges.com, a full-stack Next.js SaaS where developers practise real React technical interviews by solving timed TypeScript challenges with instant, test-based feedback. Grew it solo from zero to 2,000+ registered users, owning product, engineering, and growth.

• Reached 2,000+ registered users as a solo founder, owning the product end to end, from architecture and deployment to growth.
• Built a sandboxed test-execution server that runs submitted code in isolation and returns structured pass/fail feedback, the mechanism that makes practice feel like a real technical interview.
• Engineered the coding environment with Monaco Editor and TypeScript plus a Vim keybinding layer, and used Sandpack to render React solutions in-browser for instant visual previews.
• Modelled users, attempts, results, and progress in PostgreSQL with Drizzle ORM, and built the API layer plus secure auth, sessions, and route protection.
• Set up and operate retention infrastructure: a self-hosted Listmonk instance on a VPS sending weekly campaigns through Amazon SES.

As Lead Frontend Engineer at an early-stage startup building open-source tooling for AI workflows, I owned the frontend architecture of Design Workflow, a React + Rete.js visual editor that compiles node-based flows into the Common Workflow Language (CWL). Set the technical roadmap, led the frontend team, and established the testing foundation with Vitest and Playwright.

• Designed and built the visual workflow editor with React and Rete.js, translating node-based flows into Common Workflow Language (CWL).
• Owned the technical roadmap and frontend architecture, and led the frontend team through delivery and code reviews.
• Built a reusable component library with React, Tailwind CSS, and shadcn/ui, keeping the editor and supporting site consistent.
• Established the testing foundation with Vitest and Playwright to cover the editor and its critical flows.
• Integrated backend APIs and AI tools into the editor, enabling end-to-end AI workflow design.

At Urchin Labs I built one of the earliest ChatGPT-powered customer-service assistants (April 2023), before LangChain-style frameworks existed and with no AI ecosystem in PHP. I implemented the entire retrieval-augmented (RAG) pipeline by hand (chunking, OpenAI embeddings, Pinecone vector search, and context assembly) and wired it into WooCommerce via a custom WordPress plugin. After the startup failed to raise follow-on funding, I documented the specs and shipped it as a public beta under the name MainGPT.

• Implemented the end-to-end RAG pipeline from scratch in PHP (document chunking, OpenAI embeddings, Pinecone vector search, and context assembly), with no existing framework to build on.
• Engineered prompts and conversational memory manually to keep answers grounded in each store's content and products.
• Built the chat interfaces in React and Vue.js on top of the OpenAI API, plus a custom WordPress/WooCommerce plugin for drop-in integration.
• Shipped a headless Next.js + GraphQL site and took MainGPT to public beta with a 100-product demo store, keeping running costs at effectively zero within the OpenAI and Pinecone free tiers.
• Automated testing and deployment with Vitest, Playwright, and GitHub Actions.

Led full-stack development across Network Rail's corporate web estate — the flagship corporate site (roughly 400,000 organic Google clicks a month), microsites, single-page applications, and internal products — and set the standards and technical direction across internal teams and external agencies, cutting both internal and external cost and delivery time. In 2018, before component-driven tooling was mainstream, I introduced a Storybook-based design system reused across internal products and external agencies, and brought the bulk of previously outsourced development in-house, saving the organisation thousands of pounds.

• Led full-stack development across Network Rail's corporate web estate — the flagship corporate site (roughly 400,000 organic Google clicks per month), microsites, single-page applications in Vue.js and React, and internal products.
• Set standards and provided technical direction across internal teams and external agencies, standardising delivery to cut both internal and external cost and time, and mentoring UX developers on best practices.
• Owned the WP Engine hosting environment and CI/CD pipelines, managing deployments, staging environments, caching, and infrastructure.
• Introduced a Storybook-based design system in 2018, before component-driven tooling was mainstream — roughly 40 primitives (atoms) composed into molecules, organisms, and templates, reused across internal teams and external agencies to accelerate delivery.
• Drove 100% WCAG 2.1 AA accessibility across the corporate site and microsites, baking keyboard navigation, screen-reader support, and ARIA into the design system so compliance was enforced by default.
• Improved performance by removing unnecessary plugins and dependencies, and automated internal content workflows that were costing content managers and creators across the UK's rail routes significant time.

Two years at a UK inbound marketing agency building and optimising WordPress sites for clients including Volkswagen Financial Services and Peach Pubs. Owned the full stack of each build, from custom themes and plugins to Cloudflare DNS/CDN, with a strong focus on page speed and search performance.

• Built and maintained custom WordPress themes, plugins, and reusable libraries for client sites.
• Optimised page speed using the Google PageSpeed API on Apache to improve search rankings (SEM).
• Configured Cloudflare per client (DNS records, caching, and CDN) to improve performance and reliability.
• Developed responsive front-ends with HTML5, CSS3 (Sass and BEM), and jQuery, and integrated third-party APIs and REST services.
• Met with clients to define designs and functionality, working in an Agile team.