JD | Founding Engineer | kaizen
Location: Fully remote, within two hours of Central European Time
Type: Full-time
Day-to-day team: Josh (CTO), Michael (CEO) and you
You'll be kaizen's first dedicated engineering hire, driving the technical direction and delivery of the product across our React Native app and Python/AWS backend. You'll work alongside Josh and Michael on product decisions while taking increasing ownership of the application, infrastructure and release process as Josh focuses more deeply on our sports science and training models.
This is for someone who can make major architectural decisions, cares about the implementation details and has a nose for the work that will have the biggest impact.
The company and the role
kaizen is a load-based running training app used by more than 50,000 runners. We're live on iOS and Android, have paying subscribers and generate five-figure monthly recurring revenue. We've recently raised a pre-seed round to accelerate our progress.
Josh originally built kaizen for his own training. Michael joined as cofounder to turn it into a company. Our ambition is to build the running platform committed runners use every day.
Our next challenge is turning kaizen from a single-player training product into a platform capable of supporting different training systems, athlete-led training experiences and deeply personalised guidance— built on a runner's complete training history.
That creates substantial technical problems across historical data ingestion, wearable integrations, personalisation, training models, reliability and performance. kaizen already supports everyone from Olympians to runners completing a marathon in more than six hours.
You'll build and ship alongside Josh while taking increasing ownership of the application stack, infrastructure and release process. You'll have strong, grounded opinions and help drive decisions about why, what and how we build.
What you'll own
Own technical direction and delivery across the React Native app, Python backend, data layer and infrastructure and partner with Josh on major decisions.
Build major product features end to end, from understanding the runner's problem through to release and iteration.
Partner with Josh and Michael on what to build, what not to build and how quickly to validate it.
Improve the foundations beneath the product: architecture, testing, observability, performance, data integrity and release discipline.
Own integrations across wearables, authentication, payments, historical data sync and webhooks.
Talk directly to runners and use product data to improve activation, engagement and retention.
Raise the quality of the experience, from the underlying system to the states, interactions and details runners see.
Help shape kaizen's engineering team and practices as we grow.
In short: you'll own the full stack, from technical direction to the details runners experience.
How ownership works at kaizen
There’ll be three of us working together day to day, so we don’t need an elaborate decision-making process. Whoever owns something generally takes the lead, makes the call and sees it through. For bigger decisions, we talk it through together.
We question each other’s thinking and actively seek each other’s perspective because one of us may have context or spot something the others haven’t considered. Once we’ve gone into the right level of detail, we usually reach the same conclusion. These conversations are little and often, multiple times per day.
You’ll make most day-to-day technical decisions. Josh will retain the final say on technical matters, although, in practice, this will be exception rather than rule and you’ll have plenty of autonomy, with Josh there to challenge your thinking or add context when it’s useful.
Who you'll work with
Josh Sambrook, CTO — Sports scientist and 2:28 marathoner. Josh taught himself to code and built the original product and the proprietary training models on which kaizen runs. You'll build alongside him while he focuses increasingly on sports science and training intelligence.
Michael Keskerides, CEO — Product, growth and a 2:37 marathoner. Previously VP Product at Bitpanda and Wayflyer and Head of Product at N26.
Our stack
Frontend: React Native + Expo across iOS and Android
Backend: Python on AWS Lambda + serverless RDS
Data and product infrastructure: Firebase Auth, PostHog, Customer.io and RevenueCat
Wearable integrations: Strava, Garmin and Apple Health, plus other wearables through Terra
This is a consumer mobile product built on strong sports science and a large, complex training dataset.
Who this is for
You're a runner. You train, race and have a real relationship with the sport: enough that load, tapering, the wall and race week mean something to you. You'll be building for runners, so we think understanding them matters.
You'll do well here if you:
Have built production software that people actually use, ideally a consumer mobile or data-heavy product.
Have owned technical decisions and helped decide what to build and why, not only how to implement it.
Can move from a vague user problem to a shipped change without expecting a PM to write acceptance criteria.
Are comfortable working across React Native and Python, or can become productive in both quickly.
Know which battles to pick and when an optimisation is worth the time.
Care about product quality, including the states, interactions and copy between the headline features.
Want substantial impact and the accountability that comes with it.
Use AI development tools as a force multiplier while retaining strong engineering judgement.
Bonus, not required: Experience with Expo/EAS, AWS serverless, health or wearable APIs, production RAG or other LLM-powered workflows, or an early-stage consumer startup. A strong eye for copy and design. You've used kaizen or a competing product and have opinions about it.
Offer
Salary: 70,000 to 80,000 EUR
Equity: 1.5%-3%
Working arrangement: Full-time and fully remote, within two hours of Central European Time
How to apply
Complete our short application form: Apply to kaizen →
The process
Short written application
A 45-60 minute conversation with Josh and Michael
A 90 minute case study (covering product and engineering) — no prior preparation required
A 30 minute conversation with one of kaizen’s technical advisors
References
Offer
We'll move quickly and be transparent about timing throughout.