We're building an AI travel agent for groups: your coolest, most helpful friend, inside an app. Hal, our agent, turns a vague idea into a real trip. Not a chatbot that hands you suggestions, but an agent that orchestrates tools across flight, stay, rail and ticket inventory, for a whole group at once, in a shared itinerary everyone is editing in real time.

You would be our founding senior engineer, and the senior-most engineer in the company. Hold the technical bar at 100x scale, own the architectural calls that decide whether Halcy works at our next order of magnitude, and stay deep in the code, shipping every week alongside the three founders.

What you will mostly do

Hold the product vision in your head and translate it into the technical bets that make it real. Own the architectural calls on concurrency, AI cost, collaborative state and content delivery on mobile. Stand up the operational floor: observability, error tracking, end-to-end coverage on critical journeys, alerting. Build the speed infrastructure that lets the team ship faster as it grows. Set the bar for our next ten engineering hires.

Must have

5+ years building production systems, including at least one tour as the senior-most engineer in a small team. Deep TypeScript across the stack (React + Node or Deno) and the judgment to make architectural calls without a senior peer to bounce them off. A track record of levelling up the engineers around you. Scar tissue from at least one of: real-time multiplayer at scale, payments and bookings, or RLS-heavy Postgres at hundreds of tables.

Bonus

Mobile delivery, whether Capacitor, React Native or native. We ship to App Store and Play Store. Pragmatic on observability and security. Shipped AI-heavy products to real users, fluent in tool-use orchestration, multi-model gateways, prompt evaluation and the cost mechanics of running LLMs in production. We run Anthropic and Gemini side by side, and you should have opinions on this.

Our stack

React, TypeScript, Vite, Supabase and Postgres, React Router, TanStack Query, Tailwind, Mapbox, Capacitor, Trigger.dev, PostHog, Sentry.

The offer

1,100,000 to 2,000,000 SEK, calibrated to experience. Meaningful equity, four-year vest with a one-year cliff. Hybrid in Stockholm. Real ownership over a domain from day one.

Full role description: https://halcy.site/careers/roles/senior-engineer