Frontend Developer (Intern)

About Heidi Systems

Heidi Systems is building the data infrastructure layer for buildings and energy. We help property owners and managers digitize metering, consumption data, reporting, and billing workflows in one of the largest and most outdated infrastructure markets in Europe.

We are looking for a skilled frontend engineer who wants to own the product layer that makes complex infrastructure data legible, actionable, and fast. You will work directly on our SvelteKit application — the interface through which property managers, operations teams, and customers interact with our systems every day.

This is not a typical frontend role. You will work with real data from real buildings, build tools that handle high-volume consumption data, and collaborate closely with backend engineers and the founding team. You own what you build.

Tasks

What you will work on

• Build and improve our SvelteKit web application from the ground up


• Write strongly typed TypeScript across all layers of the frontend


• Implement server-side rendering, routing, and load functions in SvelteKit


• Build and maintain reusable UI components with Tailwind CSS and DaisyUI


• Integrate with backend APIs via oRPC and shape the contract between frontend and backend


• Write reliable tests with Vitest and JSDom


• Work with Bun as the runtime and for CLI scripting


• Improve developer tooling, code quality, and frontend reliability


• Debug real-world issues across APIs, data pipelines, and the UI layer


• Work closely with the founding team on product and architecture decisions

Requirements

Who we are looking for

We are looking for someone unusually strong, precise, and product-minded.

You should be excited about building clean, performant interfaces on top of complex data systems. You do not need to know everything already, but you should learn fast, think from first principles, and care about the end result.

You are a great fit if you:

• Have 1–2+ years of professional experience with SvelteKit and TypeScript


• Understand the Svelte reactivity model, stores, and component lifecycle deeply


• Write strict, idiomatic TypeScript — generics, utility types, no implicit any


• Are comfortable in Unix-based development environments


• Care about code quality, reliability, and shipping things that actually work


• Enjoy working close to real data and complex product requirements


• Like fast-moving environments with high ownership and responsibility


• Have a portfolio or GitHub profile you are proud of

Tech stack

SvelteKit · TypeScript · oRPC · Tailwind CSS · DaisyUI · Vitest · JSDom · Bun · Git

Nice to have

Zod · Drizzle ORM · PostgreSQL · Bun workspaces · Auth patterns (sessions, JWT, OAuth) · German: professional working proficiency · Open-source contributions

Benefits

Why join us

• Work directly with the founding team


• Own real technical projects from day one


• Learn how to build infrastructure for a fast-growing startup


• Get exposure to DevOps, data architecture, IoT, energy, and real estate infrastructure


• Help shape the technical foundation of a company tackling a huge, outdated market


• High ownership, high learning curve, high impact

Location

Berlin preferred. Hybrid setup possible.

Start

As soon as possible.

How to apply

Send us a short note, your CV or GitHub profile, and ideally one project you are proud of.