Senior AI Fullstack Engineer in Lisbon, remote worldwide. 14 years shipping — 4+ deep in web3, 2+ building AI developer tools. I build AI-native products, agent tooling, and the harnesses that keep them honest: bounded specs, isolated worktrees, evals that fail closed.

My portfolio speaks MCP. Point your agent at https://www.rubenmarcus.dev/api/mcp and let it read this résumé instead of you — setup below.

Before that: MultiVM Labs / Quantum (post-quantum L1 — main site, block explorer, and an ML-DSA-65 smart wallet on Arbitrum Stylus), Bitte Protocol (top human committer on the production AI runtime, #1 on the agent SDK monorepo, #3 on the wallet), Grover, Zup Innovation / Itaú Open Banking, Santander, and a long agency tail — Under Armour, Centauro, Samsung, Panasonic, Monsanto. Full archive →

No account, no auth, no signup. Four read-only tools plus one that emails me a brief.

https://www.rubenmarcus.dev/api/mcp

Claude — Settings → Connectors → Add custom connector, name it rubenmarcus, paste the URL. Or in Claude Code:

claude mcp add --transport http rubenmarcus https://www.rubenmarcus.dev/api/mcp

ChatGPT — Settings → Apps & Connectors → developer mode → Create, paste the URL, save.

Cursor (~/.cursor/mcp.json), and any client that takes a streamable-HTTP URL:

{
  "mcpServers": {
    "rubenmarcus": { "url": "https://www.rubenmarcus.dev/api/mcp" }
  }
}

Kimi — add a streamable-HTTP MCP server with the same URL, then run tools/list.

Codex CLI / any stdio-only client (~/.codex/config.toml) — bridge it:

[mcp_servers.rubenmarcus]
command = "npx"
args = ["-y", "mcp-remote", "https://www.rubenmarcus.dev/api/mcp"]

Then ask: What has Ruben shipped? · Summarize Ruben's experience with AI agents. · Is Ruben available right now? · Book an intro — I want to build a trading bot.

Every blog post has a .md twin: append .md to any post URL.

Three origins: a production fleet that signs transactions, a research command center, and a game harness. Full directory →

Frontier Dissector · Circuit Engineer · Density Analyst · CUDA Engineer · Pod Manager · Research Scout · Orchestrator-Reviewer · Combinator — 9 specialist roles routed across 7+ providers, with contracts, spend gates and fail-closed adapters. How it worked →

Three rules hold the loop together: the ruler is not negotiable (not "looks good" — wins or loses against a CS2 frame, by which measure), the builder never grades its own work, and the loop ends when I stop it, not when an agent declares itself satisfied. Every claim has to carry a number and a file:line.

Critics run in parallel with clean contexts; builders run in parallel across four checkouts of the repo on separate branches, plus dozens of throwaway git worktrees for one-off fixes.

Inside the loop → · The AI harness behind the game →

Versioned method, not loose prompts — 25 skills that encode how the work is actually done. Browse them →

Ralph Starter Orchestration · Autoresearch Benchmark Loop · AEO Delivery System · Benchmark Frontier Archaeology · ECDSA.fail Route Spec · Circuit Engineer Factory · ECDSA Circuit Optimization · Reversible Circuit Validation · Peak Qubit Reduction · Toffoli Reduction · ECDSA.fail Island Hunting · Multi-Agent Research Collaboration · CS Brasil Content Pipeline · Faction Pipeline · Adversarial Asset Review · Régua / Executable Quality Gate · CS Brasil PR Triage · CS Brasil Smoke Check · Gauntlet FPS · Bug Hunt · Blog Voice · Bilingual Publishing · Portfolio Cover System · Frontend Delivery Harness · Portfolio MCP

Every post ships in EN and PT, and every post has a Markdown twin for agents — append .md to the URL. All posts →

aeo.js · ralph-starter · autoresearcher · make-agent · scanrepo · elendil · new-agent · qday

• Languages — TypeScript · JavaScript · Rust · PHP · C#
• Frameworks — React · Next.js · Svelte 5 · Astro · Vue · Angular · Node · Bun
• AI & agents — Claude SDK · OpenAI SDK · AI SDK · MCP · Mastra · Ralph loops · custom harnesses
• Web3 — EVM · NEAR · Sui · Solana · Cardano · Wagmi · Viem · ERC-4337
• Infra — AWS · GCP · Vercel · Docker · Terraform · GitHub Actions · Turborepo
• Craft — Figma · Storybook · Tailwind · Three.js · GLSL

Selectively available for full-time roles and freelance contracts. Fixed-scope engagements preferred. I reply within a day or two.

• AI products & agent systems — idea or brittle prototype → product with a harness, evals, observability. 3–8 weeks.
• AI-native frontend & design engineering — a distinctive web product with an AI delivery harness that preserves quality. 2–6 weeks.
• AEO audit & implementation — make a site legible and citable to answer engines. 2–4 weeks.

ruben@rubenmarcus.dev · rubenmarcus.dev/contact · or just let your agent call book_intro.