Senior Fullstack Engineer - UK

The role

A Senior Full-Stack Engineer who owns new features end-to-end: the React interface a clinician clicks, the Python service behind it, and the data model underneath. You have shipped SaaS products inside a high-growth startup, and a slow query bothers you as much as a component that drops frames.

You know where the trade-offs live on both sides of the stack: when logic belongs in the browser and when it belongs on the server, and how a schema decision made today shows up as latency on screen in six months.

You take a loose brief and return a working, tested feature without waiting for a hand-off from another team. You read the user need behind the ticket.

You thrive in a flat, flexible team, and you pick up the specifics of building an AI product for clinicians in 190+ countries within your first weeks.

Brilliant people come from unlikely places. If you have a record of shipping hard, technically demanding products and features, whatever the industry, we want to meet you.

What you'll do

• Own features from database to browser: design the data model, build the Python service, ship the React and TypeScript interface, then watch how clinicians use it and iterate.

• Build fast, accessible interfaces in React, TypeScript and Next.js that hold up for a GP seeing twenty patients before lunch.

• Design, build and run high-performance backend services in Python, with MongoDB and Redis for storage and caching.

• Design APIs the rest of engineering and the AI team build on, and own their versioning, documentation, testing and security.

• Develop and manage message queue systems for real-time data processing.

• Shape the cloud infrastructure your features run on so they scale and stay up.

• Pair with product, design and AI engineers to turn a brief into a shipped workflow, then measure and go again.

• Write code your colleagues can read, test and extend six months from now.

What you'll need

• 5+ years of software engineering experience, with production work on both the frontend and the backend.

• Strong React and TypeScript, plus Next.js or a comparable framework. You know the browser: rendering performance, state management, accessibility.

• Python in production: building, testing and running backend services.

• Hands-on MongoDB and Redis, with sound judgment on data modeling, design patterns and trade-offs.

• Experience building and managing message queue systems at scale.

• Deep understanding of API design: security, versioning, performance and the contract between client and server.

• Application and data security knowledge on both sides of that contract.

• Experience integrating with third-party systems.

• Testable, communicative code, and fluency with source control and CI/CD pipelines.

• A record of building systems that scale, stay up under load and hold up to security scrutiny.

• Passion for AI, shown through hands-on building, prototyping or side projects.

• You default to building over requesting.

• You're confident in your thinking and open to being wrong. Great ideas win regardless of who surfaces them.

How we show up

• Build for the next decade, not next quarter. Our targets are outrageous on purpose. The world's health doesn't have the luxury of incrementalism.

• Lead, don't wait. We treat tomorrow's problems today. Sometimes we build what's needed before it's wanted, and we're fine with that.

• Follow the evidence. Trust the patient. We pursue truth relentlessly. But when the subjective and objective disagree, we treat the patient, not the numbers. Ego is a comorbidity we can't afford.

• Own the outcome. Everyone here carries the company. Raise problems with solutions, solve them end-to-end, and never be a bystander.

• Ship, measure, go again. A button today, a workflow tomorrow. More iterations beat better planning. We're precise at pace, not reckless.

• Live in clinicians' reality. Not the ideal workflow, the twenty-patients-before-lunch actual one. We build for exhausted humans, and we'd better be decent ones while we do it.

Why Heidi?

You’ll join a team measured on real-world impact, not press cycles. We live and breathe the challenges of modern health systems, and are laser-focused on exacting the change we’d like to see. We’re medicos, engineers, builders and designers who’ve felt (on every side of the equation) what non-care feels like, the moral and practical toll as a provider or receiver.

Building what we’re building isn’t always easy. Standard tech playbooks routinely fail in healthcare, and the friction of the medical system will test your perseverance. But we didn’t choose easy, we chose a purpose-driven mission that actually matters. We hold ourselves to a higher standard because healthcare demands it. If you join Heidi, you recognize that the deeper question isn’t whether AI can solve the global healthcare crisis, but whose hands will shape it.

True A-players progress extremely fast here. The nature of the scale-up game is demanding, but we value sustainable performance and mental health. You're trusted to perform, and you set your schedule. We operate on outcomes > inputs, not process theatre. We all take the bins out, metaphorically and literally.

We take care of you.

We offer health and dental cover, a £700 annual learning and development budget, a £100/month health and wellness allowance, a £500 home office budget, 26 weeks paid primary parental leave and 18 weeks paid secondary parental leave, fertility support up to £7,000, four weeks of work from anywhere per year, and serious equity.

We chose to open-source our benefits hub, if you care to take a peek.