Senior Fullstack Engineer - UK

Heidi

Get hot jobs first on Telegram

New positions appear faster in our channel

Location: London
Job Type: full-time
Work Format: 🏢 Hybrid
Salary: Not specified
Posted: October 7, 2026

Job Description

We’re Heidi.

We're building the future of healthcare by giving every clinician the earth's finest AI Care Partner. Our platform has absorbed the administrative chaos of 175 million patient visits and supported 67 million clinical hours. Today, we support 2.8 million patient sessions a week across 190+ countries, in 110 languages and over 200 specialties.

Healthcare systems are failing us; clinicians spend more time on documentation than on patients, and the human connection that makes medicine worth practicing is eroding. Our mission is simple: double the world’s capacity for care and strengthen the human connection at its heart.

We found product-market fit with a freemium medical scribe that clinicians love. Now, we're expanding. Every task a clinician hands to Heidi is a patient who feels more attended to, a health system unclogged, and a clinician who gets to be a clinician again.

We’ve grown annual recurring revenue from $1 million to $50 million in two years.

To go further, we’ve secured US$340 million: a $100 million Series C led by Blackbird, with Phoenix Court, Point72 Private Investments and Headline, alongside a $240 million growth investment led by General Catalyst’s Customer Value Fund.

If you want to join us in doing work worth shipping, jump in.

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

You will work alongside the engineers who built Heidi, shipping AI products that change how healthcare runs.

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.

🎯 Who is this job for?

This role is suitable for a Senior Full-Stack Engineer with 5+ years of production experience building and scaling SaaS products across frontend and backend systems. Required skills include React, TypeScript, Next.js, Python, MongoDB, Redis, message queues, API design and security, third-party integrations, testing, CI/CD, cloud infrastructure, and practical AI experience. The candidate should be comfortable owning features end-to-end, from data modeling and backend services to accessible interfaces, performance optimization, infrastructure, monitoring, and iterative delivery in a fast-growing product team.

💬 Potential Interview Questions

How would you design an end-to-end feature spanning a React and TypeScript frontend, a Python backend, and MongoDB?

I would start by defining the user workflow and API contract, then model the data around the required access patterns. I would implement the Python service, validation, authorization, React state and UI, followed by unit, integration and end-to-end tests.

How would you improve rendering performance in a React and Next.js application used continuously by clinicians?

I would profile before optimizing, then address unnecessary re-renders, oversized bundles, inefficient state updates and expensive list rendering. Techniques might include component memoization, route and component lazy loading, server-side rendering where appropriate, virtualization, and stable query caching.

How would you model clinical session data in MongoDB while keeping queries fast as the product scales?

I would identify the dominant read and write patterns before choosing embedding or referencing. I would use appropriate compound indexes, avoid unbounded document growth, paginate large results, and review query plans regularly to prevent collection scans.

When would you use Redis in this platform, and how would you handle cache consistency?

Redis could support short-lived caching, distributed locks, rate limiting, session data and idempotency keys. I would define clear TTLs and invalidation rules, treat the database as the source of truth, and use cache-aside or write-through patterns depending on consistency requirements.

How would you design a reliable message queue for real-time AI or clinical data processing?

I would make consumers idempotent, include correlation and retry metadata, and use acknowledgements, visibility timeouts or dead-letter queues for failures. Monitoring queue depth, processing latency and failure rates is essential for detecting backlogs and scaling consumers.

What principles would you apply when designing and versioning APIs consumed by frontend and AI teams?

I would define explicit schemas, consistent error formats, pagination, authentication and authorization requirements, and measurable performance objectives. Breaking changes should use a new version or a compatible migration path, with documentation, contract tests and deprecation timelines.

How would you secure a full-stack healthcare application handling sensitive clinical information?

I would enforce least-privilege authorization on the server, validate all inputs, protect secrets, encrypt data in transit and at rest, and avoid exposing sensitive data in logs or client-side storage. I would also apply secure headers, rate limits, dependency scanning, audit logging and regular access reviews.

How would you test a feature that includes a Python service, MongoDB, Redis, a queue, and a React interface?

I would unit-test business logic and components, use integration tests with real or containerized infrastructure, and add contract tests for API boundaries. Critical user journeys would be covered by end-to-end tests, while queue handlers would be tested for retries, duplicate messages and partial failures.

How would you design a deployment and CI/CD pipeline for services that must remain available under load?

The pipeline should run formatting, static analysis, security checks, unit tests, integration tests and build verification before deployment. I would use staged releases, health checks, observability, automated rollback and infrastructure-as-code, with backward-compatible database migrations.

How would you integrate a third-party healthcare or AI service while maintaining reliability and data protection?

I would isolate the integration behind a well-defined adapter, enforce timeouts, retries with backoff, circuit breaking and idempotency, and validate all external responses. Sensitive data should be minimized and governed by explicit consent, access controls, retention policies and auditability.

📋 Job Summary

Heidi is transforming healthcare with an AI Care Partner used across 190+ countries, helping clinicians spend more time with patients. As a Senior Fullstack Engineer, you’ll own features end-to-end, building accessible React, TypeScript and Next.js interfaces alongside Python services, MongoDB, Redis, APIs, message queues and scalable cloud infrastructure. This is a full-time hybrid role in London; salary is not specified, with serious equity and a strong benefits package including health and dental cover, learning and wellness budgets, parental leave and flexible work-from-anywhere time. Apply to ship meaningful AI products at exceptional scale, work with a high-impact team and help double the world’s capacity for care.