Senior Lead Software Engineer- Back End- Madrid

Job Responsibilities

• Build and maintain integrations with digital asset providers and infrastructure (on ramp/off ramp), optimising for security, stability and escalability.
• Work with the Product team to understand user needs and follow an Agile SDLC to develop and deliver product features. Our stack is Java/Springboot with a bit of Kotlin, DynamoDB, Aurora/MySQL and AWS.
• Participate with the rest of the team in designing how our architecture needs to evolve to meet our needs. We use ADRs as part of our decision-making process, and our architecture is microservices running on Kubernetes with heavy use of Kafka and event-driven design — a natural fit for streaming real-time market data and trade events.
• Partner with Compliance, Risk, and Operations to ensure integrations meet regulatory, security, and controls requirements relevant to digital assets (e.g., transaction monitoring, wallet screening, key-management controls).
• Take ownership of tasks from the estimation stage right through to release and post-production.
• Identify, troubleshoot and resolve existing or newly identified prioritised defects — with particular care around anything touching balances, order flow, settlement, or asset movement, where correctness is non-negotiable.
• Write tests for all code you deliver and adhere to best practices/standards, ensuring high-quality code. Given the financial and irreversible nature of on-chain transactions, expect a strong emphasis on deterministic, well-tested, and auditable code paths.
• Take ownership of, or assist others with, releases and associated processes (we try to deploy as often as possible).
• Participate in code reviews, ensuring high code quality and continuous development and learning for yourself and your colleagues.
• Be someone who enjoys knowledge sharing and is keen to attend and participate in the many skill-share sessions we regularly hold across the wider Engineering department.
• Propose/contribute/collaborate on Technical Initiatives — improving and evolving the existing codebase and toolset.
• Help ensure we focus on solving the essence of the problem rather than merely dealing with the symptoms.
• Required qualifications, capabilities and skills
• English working proficiency is a must; you will be working with the team in London.
• Hands-on experience with exchange, brokerage, custody, wallet, or settlement systems for digital assets.
• Drives adoption and governance of approved AI-assisted engineering practices across teams to improve code quality, delivery speed, and operational outcomes (e.g., AI-assisted code review/refactoring, test acceleration, release readiness, incident/root-cause analysis), while establishing measurable validation standards (secure coding, peer review, automated testing) and promoting reuse of proven patterns and automation within the SDLC/TLM toolchain.
• Applies knowledge of tools within the Software Development Life Cycle toolchain, including approved AI-assisted development and automation capabilities, to improve the value realized by automation at scale.
• Solid working understanding of digital-asset fundamentals: blockchains, wallets, public/private keys and signing, transactions and fees (e.g., gas), tokens (e.g., ERC-20 and equivalents), and the distinction between custodial and non-custodial models.
• Experience with smart contracts and/or reading on-chain data (e.g., Solidity, web3 libraries, node providers such as Infura/Alchemy, or running your own nodes).
• Familiarity with how connectivity with blockchain networks and nodes work (e.g., Bitcoin, Ethereum and EVM-compatible chains, Layer 2s), including transaction construction, broadcasting, monitoring for confirmations/reorgs, and reconciliation of on-chain and off-chain state.
• Awareness of the regulatory and compliance landscape for digital assets (e.g., AML/KYC, travel rule, market-abuse considerations).
• You have a product engineer mindset and a track record of delivering high-quality software that adjusts to business and product needs to provide a great user experience in a timely manner.
• Experience with a JVM language (Java/Scala/Kotlin) and Springboot.
• Experience designing systems from scratch as well as evolving existing architectures to achieve new goals, both serverless and managed in the cloud.
• Hands-on experience designing and implementing event-driven architectures with different message brokers, including Kafka — ideally applied to high-throughput, low-latency data such as market or trade feeds.
• Experience integrating with third-party financial or trading APIs (REST, WebSocket, and/or FIX), including handling rate limits, authentication/signing schemes, reconnection, and idempotency.
• Experience with monitoring and alerting to maintain a production environment — with an appreciation that in trading/crypto contexts, downtime and latency have direct financial consequences.
• Good understanding of REST and what it means to work with APIs.
• Experience with Git flow.
• Good communication skills; you can work well within a delivery team and manage interactions with other parts of the organisation, such as Product, Operations, Compliance, and Risk.
• Curious about new ways of working and open to different approaches and ideas.
• Proactive and willing to help others and put forward ideas.
• Preferred qualifications, capabilities and skills — nice to haves
• Familiarity with trading concepts such as order books, order types, matching, market/limit orders, and settlement lifecycles.
• Experience with DynamoDB and/or Aurora.
• Experience in the FinTech, trading, or digital-asset sector.
• Experience developing a multi-country product with multiple localizations and currencies (crypto or fiat).
• Show us your Github/Stack Overflow/app portfolio — bonus points for crypto/blockchain projects!
• #ICBCareers #ICBEngineering