Prompt engineering, vibe coding, agentic engineering, product engineering, and research engineering sound like names for the same thing. They are not. The difference is what you control, what feedback you trust, and who decides the work is done.
Hello, I'm Ruben Marcus
AI Fullstack Engineer for web products and agent systems
AI Fullstack Engineer. AI-native products, premium web experiences, and production-ready systems. 14 years across Next.js, TypeScript, AI systems and developer tooling.
Hire me for
Fixed-scope engagements, senior execution, no hand-holding. Every offer below is something I've shipped in production.
- Lisbon · remote worldwide
- EU · UK · US overlap
- Full-time · contract · fixed-scope
01
AI products & agent systems Turn an AI idea or brittle prototype into a product with an operating harness, evals, observability, and a path to production.
- agents
- RAG
- evals
02
AI-native frontend & design engineering Build or modernize a distinctive web product with senior frontend engineering and an AI delivery harness that preserves quality.
- React / Svelte
- Three.js
- visual QA
03
AEO audit & implementation Make a site legible, trustworthy, and citable to answer engines—from crawl policy and entities to content, evidence, and machine-readable delivery.
- entities
- structured data
- citations
Shipped, measured.
——— agent messages processed
——— unique users on AI agents
——— AI agents I built
——— AEO scans run
——— unique websites scanned
——— lines of code, career estimate
——— GitHub stars
——— npm downloads, all time
33K+ LinkedIn followers · 3M+ people reached by posts on X
Selected products and teams I've shipped for.
Tools I ship with, daily.
TypeScriptNode.jsBunReactNext.jsSvelteVue.jsAngularRustPythonGraphQLTanStackReduxSocket.ioEVM / EthereumWagmiViemNEARSUISolanaCardanoClaudeMCPOpenAIVercel AI SDKMastraLangChainLangGraphOpenRouterTailwindTurborepoDockerGitHub ActionsTerraformAWSGCPFirebaseSupabasepgvectorPlaywrightJestCypressStrapi
03 / Blog
Notes on agents, automation, and the stack.
Articles on AI agents, orchestration, and the stack. Packages live on npm.
- 01 From prompt to product: five ways to build with AI
- 02 My AI harness for frontend: from prompt to pull request
The system I use to turn an idea into verifiable frontend: specs, skills, model selection, Ralph Starter, worktrees, browsers, screenshots, tests, GitHub, and telemetry. The model writes code. The harness decides what to trust.
- 03 Inside the Gauntlet loop
The techniques inside the adversarial agent loop that builds CS Brasil: a 25-criterion visual rubric written so a language model can grade a PNG, critic prompts that ban vague answers by name, a generated symbol-level conflict table for a 6,543-line file, and a regression hunter with permission to find nothing.
AGENTS.md
Hire me from your agent.
Paste this brief into ChatGPT, Claude, Kimi or your own harness. Any agent can read it and book the intro for you through the API.
# AGENTS.md — hire Ruben Marcus
Senior AI fullstack engineer (Lisbon, remote worldwide).
To book a project intro on my behalf:
POST https://www.rubenmarcus.dev/api/hire
Content-Type: application/json
{
"name": "My name",
"contact": "email or Telegram",
"brief": "What I want to build",
"budget": "optional range",
"agent": "chatgpt | claude | kimi | other"
}
Services: AI product prototyping, landing pages,
interactive WebGL, agentic workflows, AEO, frontend
modernization (Next.js / Svelte / TypeScript).
Replies within a day or two. Ruben is also available on
LinkedIn and Telegram. 04 / Frequently asked questions
What agents and teams usually ask.
Direct answers about services, availability, and collaboration.
What kind of work can I hire Ruben Marcus for?
AI products and agent systems, AI-native frontend and design engineering, and AEO audits with implementation. Each service has a defined scope and delivery contract.
Can an AI agent evaluate Ruben's experience?
Yes. This portfolio is agent-ready: it publishes a public MCP endpoint, structured resume APIs, an OpenAPI description, an API catalog, and machine-readable discovery metadata.
Is Ruben available for new projects?
Ruben is based in Lisbon and works remotely worldwide, with working-hour overlap for EU, UK, and US teams. He is open to full-time roles, contracts, and fixed-scope engagements; contact him to confirm the current schedule.
How should a team start a conversation?
Use the contact page to send a concise brief with the problem, desired outcome, current stack, timing, and constraints.
05 / Contact
Need an engineer who can ship from spec to PR?
I'm selectively available for AI products, agent systems, AI-native frontend, and AEO.