Fullstack Developer

The Hub/Danske Bank; København; On-site; DKK 700,000 - 900,000; Full time

Benefits offered by this job

Hybrid work Copenhagen

25 days holiday

Flexible core hours 09:00–16:00

Small, dedicated team of 11

Job summary

Geniebelt is seeking a Fullstack Developer to own backend and frontend work across Ruby on Rails and React/TypeScript, in an AI-native, startup-like team based in Copenhagen.

You will ship features end-to-end, modernise the platform, and own core product areas with guidance from senior engineers in a small, results-driven environment.

Qualifications

• 4–7 years of hands-on Ruby on Rails and React/TypeScript experience.
• AI-native working approach, including using coding agents.
• Strong PostgreSQL knowledge and relational modelling.
• Docker and Git in collaborative workflows.
• Ability to reason about trade-offs in consistency, availability and performance.
• Fluent English communication.

Responsibilities

• Develop backend APIs with Ruby on Rails for web and mobile clients.
• Build frontend UIs with React and TypeScript.
• Modernise stack by updating Ruby, Rails, TS, and React.
• Own features and collaborate with senior engineers to expand product areas.
• Write clean, testable code and perform root-cause analyses when issues arise.
• Ship features end-to-end across the full stack.

Skills

Ruby on Rails

React

TypeScript

PostgreSQL

Docker

Git

AI agents

English communication

Tools

Kubernetes

Job description

Are you eager to join an agile development company with no B.S. and no bureaucracy? Do you thrive in a trust-based, transparent, startup-like environment where you are encouraged to have your say and to own the outcome?

At Geniebelt, we are on a mission to transform construction by accelerating repeatable build. We empower builders to scale excellence through repeatable build: turning every project into a foundation for the next, powered by collaborative, repeatable workflows that drive consistency, predictability, and growth. Our platform handles more than 150,000 weekly updates for thousands of active users worldwide, and we do it with a small, dedicated company of 11.

We are looking for a Fullstack Developer who is comfortable in Ruby on Rails and React / TypeScript, and who wants to grow real ownership of the product from database to UI, working alongside experienced engineers who know the platform inside out.

Our ambitions are big: to be the recognised category leader in Europe, the #1 platform for repeatable build, and a high-performing team with a challenger mindset running a scalable operating model that drives profitable growth. This role is central to getting there.

The role

You will work across the full stack, shipping features end-to-end and helping modernise a platform that thousands of builders rely on every day.

• Backend (Ruby on Rails): Design and build reliable backend functionality and APIs consumed by our web and mobile clients.
• Frontend (React / TypeScript): Build clean, responsive interfaces that make complex construction workflows feel simple.
• Modernisation: Help bring the platform to the latest Ruby, Rails, TypeScript, and React, retiring obsolete libraries and legacy code as we prioritise stability and a great customer experience.
• Ownership: Take ownership of features (and, over time, core product areas) with support from senior engineers who know the platform deeply.
• Quality: Write clean, testable code and perform proper root-cause analysis when things break.

How we build (AI-native)

We are building an AI-native engineering team, and we treat modern coding agents as a core part of how we ship. Not a novelty on the side. In practice, that means you spend less time hand-typing boilerplate and more time as a conductor: framing and specifying work clearly, orchestrating AI agents to draft it, and then reviewing, integrating, and merging the result to a high standard. The human owns the judgment and the quality bar; the agents accelerate the throughput.

We are looking for someone who genuinely believes in this way of working and is already doing it, or is hungry to. If you love turning a well-framed problem into shipped, reviewed, production-grade code with AI as a force multiplier, you will feel right at home.

What you bring

• Solid, hands-on experience (roughly 4–7 years) with Ruby on Rails and React / TypeScript. You can genuinely work across the stack.
• An AI-native way of working: you already use coding agents as part of how you build, and you are comfortable being the reviewer and integrator of AI-generated work.
• Solid knowledge of PostgreSQL and relational data modelling.
• Comfort with Docker and Git in a collaborative workflow.
• Growing systems thinking: you are building good judgment on trade-offs between consistency, availability, and performance.
• Review judgment: you can tell genuinely good code from plausible-looking code. Whoever, or whatever, wrote it.
• Communication: fluent in English, able to share knowledge and support the team.

You don't need to be the most senior person in the room. You will work alongside engineers who have built and scaled the platform, and we will back you to grow into broader technical ownership.

Bonus: exposure to cloud / AWS, Kubernetes, or CI/CD is useful, but not essential for this role.

How we work (and who thrives as a genie)

Our culture rests on four things, and we hire for them as much as for skills:

• Winning mindset — play to win, know your goals, raise the bar, play the right game.
• High agency — step up, take initiative, own it, get it done.
• Play together — bring your passion, have each other's back, value feedback, enjoy the ride.
• Curiosity — stay open, explore new perspectives, try novel ways, learn fast.

In practice, that means you take responsibility when something breaks — regardless of where it started; you make decisions based on context and requirements, not dogma; and you improve existing code instead of working around it.

Benefits & culture

• Location: Hybrid setup in our Copenhagen office (Tuesday and Wednesday are fixed in-office).
• Holiday: 25 days of paid holiday, plus 5 additional "feriefridage".
• Flexible hours around our core window of 09:00 to 16:00.
• Real impact: a genuine opportunity to "punch above your weight" in a small, dedicated team of 11.
• Social: monthly social gatherings and outings with a relaxed, fun team.

Start date

We are hiring now and would love for you to start as soon as possible.