Senior Backend Engineer

About Dolfin

We're building the agentic financial ops layer for SMB platforms. Fintechs, vertical SaaS, banks, and PSPs use Dolfin to embed AI-native financial ops agents (invoicing, bills, expenses etc) directly into their products. White-label, API-first, production-ready.

Our agents live in production with real SMBs. We're live and moving fast: signed platform clients including a unicorn, pipeline in the $M's, and part of Balderton's latest 'Launched' cohort.

We're looking for a Senior Backend Engineer to build the core of the platform alongside the founding team. This is a deep, heads-down build role: design and ship the systems everything else runs on, and own them in production.

What you'll be doing

• Design, build, and own core backend services, APIs, and infrastructure.

• Build the event-driven, multi-tenant systems partners embed into their products.

• Ship LLM and agentic workflows into production, where correctness and reliability actually matter.

• Own the hard parts: data models, state machines, failure modes, audibility, performance.

• Take features from spec to production and stand behind them once live.

• Partner directly with the founders on architecture and technical trade-offs.

How we build

• Production-first. If it isn't live and reliable, it isn't done.

• Correctness is non-negotiable - reliability, auditability, and failure modes come first.

• Pragmatic, not dogmatic. Boring tech where it counts, bold choices only where they differentiate.

• AI-native. LLMs as infrastructure, not features.

• Built to embed. API-first and multi-tenant from the ground up.

• Small team, high trust. Judgement over process, every time.

What you'll need

• 4+ years shipping and owning production backend systems.

• A fintech background is essential - ideally fintech API infrastructure (payments, ledgers,. accounting, banking, open finance). You've built or integrated financial APIs and understand what breaks.

• Deep experience with event-driven, multi-tenant backends and the correctness demands of money movement.

• Genuinely autonomous: take an ambiguous problem, make the call, ship it.

• Comfortable operating without structure, and creating it.

• Able to jump into frontend when a feature genuinely needs it.

Bonus: hands-on with LLMs/agentic systems, payment or open-banking integrations (Stripe, Yapily), or time at an API-led fintech (Codat, TrueLayer, GoCardless, Modulr).

Who this is for

Engineers who want to go deep on hard backend problems. Builders who've shipped zero-to-one and owned it in production. People who make the call rather than wait to be told.

Not for: fully remote candidates, big-company pace, or anyone who needs tightly scoped tickets.

Why us

• Genuine early-team role with meaningful equity.

• Real production AI systems, not experiments.

• Deep ownership of the systems the whole product runs on, and a hand in shaping the architecture and engineering culture from day one.

Southbank, London, in-person. Full-time. Let's go!