Production backend systems
Java 17/Kotlin, Spring Boot, REST/OpenAPI, PostgreSQL, distributed workflows, authentication, and CI/CD for business-critical services.
Alejandro Saez Castells / Valencia, Spain
Senior Backend &Smart ContractEngineer forproduction-gradeWeb3 systems.
I build backend services, smart contracts, DeFi infrastructure, signed-intent protocols, blockchain integrations, and workflow systems where roles, permissions, state, deadlines, and reliability matter.
Open to remote backend, smart contract, protocol, and Web3 roles across EMEA and international teams.
15+ yearsengineering background
4+ yearsbackend, full-stack & Web3 focus
Java / TSSpring Boot and Node.js systems
Solidity / EVMprotocols, contracts, and integrations
portfolio/system-mapProduction mindset
01 / backend systemsAPIs, identity, persistence, integrations
Java, Spring Boot, Node.js, PostgreSQL, Keycloak, OpenAPI, CI/CD.
02 / protocol systemsDeFi, signed intent, state machines, settlement, invariants
Solidity, EVM, Foundry, ERC-4626, EIP-712, access control, fork testing, fuzzing.
03 / operational softwareInterfaces connected to real processes
Marketplace, aviation, travel, identity, workflow, and developer-tooling systems.
type ProductionSystem = {
boundaries: "explicit";
state: "reliable";
failureModes: "designed";
operations: "observable";
};Core systemsBackend architecture, DeFi protocols, signed-intent systems, and smart contracts
Integration layersIdentity, wallets, signatures, providers, databases, blockchain data, and user flows
Operational domainsFintech, Web3 infrastructure, travel, logistics, marketplaces, and workflow automation
What I bring
Engineering depth across backend, protocols, and real operations.
The differentiator is not a longer technology list. It is the ability to model a real process, define reliable boundaries, and carry it through contracts, services, integrations, and product flows.
Identity & security engineering
Keycloak, OAuth 2.0, OIDC, JWT, federation, organization-aware authorization, role/claim synchronization, and security-sensitive state transitions.
Smart contracts & protocols
Solidity/EVM, Foundry, DeFi integrations, signed-intent protocols, access control, fuzzing, stateful invariants, and explicit threat boundaries.
Reliability-first ownership
Industrial automation discipline applied to software: model state clearly, design failure paths, automate validation, investigate production evidence, and ship durable fixes.
Selected work
DeFi infrastructure, protocol security, and production ownership.
Adaptive Yield demonstrates ERC-4626 vault engineering, Aave V3 and Morpho integration, constrained rebalancing, Base fork tests, fuzzing, and invariants. OrderForge shows signed-intent settlement and adversarial smart-contract design. CookingPro anchors the portfolio in sustained ownership of a live two-sided product.
DeFi protocol infrastructureFlagship DeFi
USDC vaultBounded strategiesIdle liquidity floor
Adaptive Yield
DeFi protocol engineering where ERC-4626 accounting, external-strategy trust boundaries, liquidity, risk constraints, and adversarial testing have to agree before any capital is considered.
A risk-aware ERC-4626 USDC yield-optimization protocol on Base with Aave V3 and Morpho adapters, constrained rebalancing, fork testing, fuzzing, and stateful invariants.
Signed-order protocolFlagship protocol
protocol / signed-intent settlementOrderForge
v1.0.001 / Maker intentEIP-712 OrderChain + verifying contract bound
02 / Protocol coreVerify · bind · account
EOA / ERC-1271nonce lifecyclepartial-fill math
03 / Atomic settlementMaker ↔ TakerDirect ERC-20 transfers · zero intended custody
Typed hashing
Replay protection
Stateful invariants
OrderForge
Signed-order protocol engineering where cryptographic intent, lifecycle state, settlement math, and adversarial testing all have to agree.
A non-custodial EIP-712 signed limit-order settlement protocol with partial fills, ERC-1271 smart-wallet signatures, replay protection, and stateful Foundry invariants.
Production mobile productFlagship production
CookingOne marketplace, two product experiences
Android iOS Tablet
Customer app
Kitchen operations
CookingPro
Production restaurant operations and customer ordering across three mobile applications.
A production restaurant-management and customer-ordering platform spanning an Android management application plus Android and iOS customer experiences. I contributed across product functionality, mobile workflows, supporting APIs, quality, and releases.
Hackathon builds
Focused Web3 products built around explicit payment controls.
Two compact public builds show policy-controlled agent payments and self-custodial team treasury workflows without overstating their deployment scope.
Agentic paymentsOpen-source Web3 prototype
Policy allow / denyRequest-bound receiptCasper proof
CSPR AgentPay Guard
A policy-controlled payment firewall for autonomous agents using HTTP 402 and Casper Testnet proof recording.
A policy layer binds payments to exact requests, applies allowlists and spending limits, rejects replay attempts, and exposes a Casper verification path without giving the hosted app access to private keys.
My contribution: Designed and built the policy engine, HTTP 402 flow, Casper integration path, audit trail, tests, and reviewer-facing dashboard.
Programmable paymentsOpen-source hackathon build
450 USDt treasuryCaptain + TreasurerWDK policy proof
CupTreasury
A self-custodial football team treasury with deterministic approvals and WDK-guarded payment intents.
The prototype models squad contributions and match-day expenses, then turns role-based approvals into exact payment capabilities with policy simulation and safe no-broadcast signing.
My contribution: Designed and built the treasury product, Captain/Treasurer approval model, guarded payment-intent flow, WDK proof surface, and automated verification.
Developer tooling
Local infrastructure for faster smart contract iteration.
Fondant extends the portfolio beyond application delivery into repeatable Casper development and testing workflows.
Blockchain toolingDeveloper tooling
Deploy inspectionLocal node controlCCTL workflow
Fondant
A Ganache-like local testing environment for Casper smart contract workflows.
A blockchain application suite and Ganache-like testing environment for the Casper blockchain, packaging CCTL functionality in a Docker-based UI to improve local development and testing workflows.
Technical focus
Technology grouped by the systems it helps deliver.
My current focus is the intersection of backend systems, DeFi and protocol engineering, smart contracts, and real-world operational workflows.
Smart contracts & protocol engineering
Signed intent, settlement, protocol state machines, token flows, access boundaries, and adversarial smart-contract verification.
Backend systems, identity & APIs
Production services, persistence, authentication, federation, asynchronous processing, external integrations, and operational backend design.
Full-stack & mobile product development
User-facing products that connect interfaces, data, identity, operational workflows, mobile platforms, and blockchain interactions.
Data, delivery & infrastructure
Persistence, containerized environments, CI/CD, deployment workflows, observability, documentation, and third-party integration boundaries.
Engineering background
Industrial automation shaped how I build software.
My industrial automation background gives me a practical systems mindset: model the process clearly, handle edge cases, keep state reliable, and design for real operational constraints.
Model the real workflow first
Start from actors, constraints, state transitions, and operational risk before choosing the technical shape.
Keep core logic explicit
Make contracts, APIs, and integration boundaries readable enough to review, test, and maintain.
Design for failure at the edges
Treat providers, wallets, networks, identity checks, and external data sources as reliability boundaries.
Own the system after merge
Treat rollout, observability, incident analysis, documentation, and maintainability as part of engineering rather than follow-up work.
Explore
Read the case studies or review the public engineering profiles.
Architecture, technical decisions, reliability considerations, and project proof are documented throughout the site.