Onmo
Senior Software Engineer - Core Systems
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About the Role
We're building the core banking capabilities that power everything at Onmo - the systems that hold accounts, move money, calculate interest, and generate statements. The Core Systems team owns these capabilities end-to-end, along with the shared services the rest of engineering builds on.
You'll help build new core systems from the ground up as we grow and pursue a UK banking license, evolve the services every team depends on, and set patterns that get adopted across engineering. Your work reaches customers through every journey at once.
Tech Stack
- Backend: Node.js / TypeScript on AWS — serverless (Lambda, API Gateway, DynamoDB, S3, SNS, SQS, EventBridge, Kinesis) and containerized compute (ECS, ECR, EC2), with more of the latter as our core systems grow
- Frontend: React / Next.js
- Infrastructure: Terraform, GitHub Actions CI/CD, Docker
- Observability: Datadog, Grafana, Prometheus, Loki
Responsibilities
- Design, build, and run core banking capabilities - money movement, interest, statements, reconciliation - that are accurate, monitored, and dependable
- Build new core systems and migrate off vendors safely: parallel runs, reconciliation, clean cutovers
- Own and evolve our shared services: modernize patterns, improve reliability and performance, keep them easy to build on
- Set patterns that get adopted across engineering through our RFC process - landed as libraries, guides, and paved paths, not one-off fixes
- Review other teams' contributions to core-owned services: quick, helpful reviews that keep the bar high without blocking anyone
- Write code that sets the standard - tested, correct, documented - and mentor engineers across the function
- Help shape technical direction with the tech lead: architecture, build-vs-buy decisions, engineering standards
- Make our systems self-serve, so other teams can ship on them without needing us
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About You
Skills / Attributes
- You care about correctness - edge cases, idempotency, retries, reconciliation - because this code moves money
- You're comfortable designing distributed, event-driven systems and reasoning about failure modes and data consistency
- You'd rather build the paved path than fix the same problem five times, and you write things down so others can follow
- You communicate clearly with engineers, product, and business stakeholders, and review others' work firmly and kindly
- You're pragmatic in a startup: happy across greenfield builds and a legacy estate mid-migration, choosing boring technology when boring is right
- You want real ownership of foundational systems
- Can operate effectively under ambiguity
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Qualifications / Experience
- Proven experience as a senior backend or full-stack engineer building and running distributed systems in production
- Strong Node.js/TypeScript and AWS, across serverless and containerized workloads
- Infrastructure as code with Terraform; CI/CD as a habit
- A track record of raising engineering standards around you — through reviews, patterns, tooling, or mentoring
- You write clean, tested, maintainable code and leave systems more understandable than you found them
Bonus Skills
- Fintech, banking, payments, or ledger experience - reconciliation, card rails, double-entry accounting
- Experience with core system migrations or vendor replacements
- Experience getting real leverage from AI-assisted development tooling
- Start-up experience
FCA Compliance & Consumer Duty
At Onmo we all take collective responsibility for our individual roles in creating the best outcomes for our customers. In this role that involves:
- Following the FCA Conduct Rules:
- You must act with integrity
- You must act with due skill, care, and diligence
- You must be open and cooperative with the FCA, PRA, and other regulators
- You must pay due regard to the interests of customers and treat them fairly
- You must observe proper standards of market conduct
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