Senior Backend & Smart Contract Engineer
Production backend systems · Smart contracts & Web3 · Cross-platform product engineering

Valencia, Spain · Open to remote opportunities across EMEA and international teams

I build backend services, smart contracts, blockchain integrations, and production applications where roles, permissions, money, state, deadlines, and reliability matter.

My background spans more than 15 years of engineering, from industrial automation and operational systems to backend, full-stack, mobile, and blockchain development. I bring the same mindset to software that production environments demand: explicit state, controlled failure modes, observable operations, strong testing, and designs that remain understandable under pressure.

My current focus is the intersection of:

• Backend and identity systems — APIs, authentication, federation, persistence, integrations, and CI/CD
• Smart contracts and protocol integrations — permissions, state machines, DeFi routers, token flows, deadlines, and security boundaries
• Programmable payments — agent spending policies, payment intents, wallets, receipts, and authorization rules
• Production product engineering — cross-platform applications, marketplaces, operational interfaces, testing, and release delivery
• Real-world workflows — aviation, travel, food marketplaces, team finance, identity, and operational automation

A production mobile marketplace connecting customers with nearby local kitchens.

Cooking is a two-sided product composed of an Android and iOS customer application and a dedicated Android manager application used by kitchens for daily operations.

I contribute across the customer application, the store-facing manager experience, and supporting API behaviour. My work includes marketplace discovery, maps, menus, favourites, cart state, authentication, sharing, order UX, store order workflows, notifications, product availability, automated testing, release configuration, and production troubleshooting.

The project requires maintaining consistent product state across customer and kitchen workflows while handling Android- and iOS-specific behaviour, mobile failure states, native dependencies, and app-store delivery.

Demonstrates: production mobile engineering · two-sided marketplaces · cross-platform reliability · operational software · state management · automated mobile testing · release readiness

Stack: React Native · Expo · TypeScript · Expo Router · TanStack Query · Jotai · Supabase · EAS Build · Jest · Maestro

Case study · Product website · Customer app · Google Play · Customer app · App Store

Policy-controlled HTTP 402 payments for autonomous AI agents.

An agentic-payment system where an autonomous agent can purchase a protected API response only when a deterministic spending policy authorizes it. Payments are bound to exact requests and protected through merchant allowlists, spending limits, expiration checks, audit events, and replay prevention.

The project includes a TypeScript monorepo, protected API, policy engine, agent runner, dashboard, Casper adapter, and an Odra smart contract for recording proof data on Casper Testnet.

Demonstrates: agentic commerce · HTTP 402 · policy engines · request-bound receipts · replay protection · Casper Testnet · on-chain proof recording

Stack: TypeScript · Node.js · Next.js · Rust · Odra · Casper · Vitest

Live demo · Source code · DoraHacks submission

A self-custodial treasury for football teams, squads, and fan groups.

CupTreasury replaces contribution reminders and expense approvals managed through WhatsApp with a structured treasury workflow. Captain and Treasurer approvals are transformed into exact, one-time payment capabilities that can be evaluated through Tether WDK policies.

The project includes contribution tracking, match-day expense requests, role-based approvals, PaymentIntent authorization, WDK policy simulation, safe no-broadcast signing, proof artifacts, automated tests, and a judge-facing verification flow.

Demonstrates: programmable payments · self-custody · approval policies · capability-based authorization · Tether WDK · security boundaries

Stack: Next.js · TypeScript · Tether WDK · React · Vitest · GitHub Actions

Live demo · Source code

A security-aware Uniswap V2 integration with slippage protection and reproducible fork testing.

SwapGuard demonstrates the complete ERC-20 swap lifecycle: router quotations, exact-input swaps, minimum-output protection, transaction deadlines, temporary router allowances, direct output delivery, and transaction receipt handling.

The project includes a focused Solidity integration contract, behavioral mocks, unit and fuzz tests, pinned Arbitrum fork tests against real deployed contracts, local Anvil tooling, CI, and a React interface built with wagmi and viem.

The public deployment is an interactive portfolio preview. Real swap execution is available through the reproducible local Arbitrum fork without using real funds.

Demonstrates: DeFi integration · Uniswap V2 · ERC-20 allowances · slippage protection · router trust boundaries · fork testing · wallet transaction UX

Stack: Solidity · Foundry · OpenZeppelin · React · TypeScript · wagmi · viem · Arbitrum · Vercel

Interactive demo · Source code

Winner of the Blockchain-based Turnaround Checklist challenge at Decode Travel Barcelona 2025.

A smart-contract-backed aviation workflow created with Camino Network and Vueling. Each aircraft turnaround is modeled through task ownership, role permissions, completion states, operational deadlines, SLA and KPI computation, certification, and ERC-721 reward badges.

The project translates a real multi-actor operational process into explicit, auditable smart-contract state transitions.

Demonstrates: operational workflow modeling · smart-contract state machines · deadlines · KPIs · certification · tokenized incentives

Stack: Solidity · TypeScript · Next.js · Camino Network · IPFS · ERC-721

Case study · Source code

A Ganache-like local development environment for Casper applications.

Fondant packages Casper CCTL functionality into a Docker-based application suite with interfaces for accounts, blocks, deploys, events, logs, and local RPC workflows.

It was designed to shorten the feedback loop for developers building and testing Casper smart contracts without relying entirely on shared networks.

Demonstrates: blockchain developer tooling · local infrastructure · Dockerized environments · RPC integration · developer experience

Stack: TypeScript · Rust · Docker · Docker Compose · CCTL · Casper

Case study · Source code

Alongside my public Web3 and product work, I build backend and identity systems using Java, Spring Boot, PostgreSQL, Keycloak, REST APIs, OpenAPI, Docker, Gradle, and CI/CD.

My professional work includes:

• Identity federation, SSO, authentication flows, and role synchronization
• Keycloak extensions, authenticators, event listeners, and client policies
• REST and gRPC service design
• Database modeling and Flyway migrations
• External provider and blockchain integrations
• Authorization and account lifecycle rules
• Automated unit and integration testing
• Production debugging, system upgrades, and deployment workflows

• Start with the actors, rules, constraints, and failure modes—not the framework.
• Keep contract, application, and API state transitions explicit and testable.
• Treat authentication, wallets, signatures, providers, mobile platforms, tokens, and external protocols as reliability boundaries.
• Separate demonstrable functionality from assumptions, simulations, and future production work.
• Use blockchain where it provides verifiable state, traceability, programmable authorization, or meaningful automation.
• Test isolated behavior with mocks and external integrations against reproducible environments.
• Validate critical product journeys across the platforms and device states where they run.
• Document architecture, trade-offs, trust assumptions, limitations, and production-hardening requirements.

• Autonomous-agent payments and HTTP 402 workflows
• Policy-controlled wallets and programmable payment authorization
• DeFi protocol integrations and secure token flows
• Reproducible mainnet-fork testing
• On-chain proof and audit systems
• Blockchain-backed operational workflows
• Reliable cross-platform applications connected to backend and identity systems

I am open to remote opportunities involving senior backend engineering, smart contracts, DeFi integrations, blockchain platforms, Web3 infrastructure, programmable payments, production mobile products, and technically ambitious product development.

Portfolio · LinkedIn · Contact