About this role
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 licence, 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 containerised 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: modernise 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
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
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 containerised 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