Full Stack Developer

We're a venture-backed ad tech startup building the next generation of AI-powered advertising technology, spun out of a performance marketing and creative agency that runs live campaigns every day. Every feature is proven against live campaigns in our agency before it ships. The platform connects to multiple ad channels, pulls in large volumes of performance data, and lets brands, agencies, and performance marketers create and manage campaigns directly. Reliability and correctness are critical: one bug can affect budgets, bids, or reporting. Our team is distributed across Europe, our investors are US-based, and our customers are global. As a Full Stack Developer, you'll work end-to-end across our platform - from database schema and row-level security to API endpoints and UI components. You'll operate in a heterogeneous, multi-repository codebase spanning different languages and architectures, integrate LLMs, and build the agentic workflows that power our analysis features. What you'll do Ship features end to end: schema and RLS, API layer, UI component.Build the agentic workflows behind our analysis features — LLM-powered nodes, streaming results to the UI, sane behaviour when a model times out or refuses.Model the analytics domain and the multi-channel audit layer so channel-specific quirks stay at the edges and don't leak through the system.Own tenant isolation: row-level security, JWT claims, organisation scoping.Keep query performance honest as data volumes grow — schema design, indexing, reading plans before they become incidents.Work autonomously across repositories, matching the conventions already in each one rather than importing your own. What you'll work with Frontend: TypeScript 5 (strict), Next.js 16 (App Router), React 19, Tailwind CSS v4, shadcn/ui.Backend: Python (async/await, Pydantic v2), FastAPI + Uvicorn, SQLAlchemy 2.0 async + Alembic, asyncpg, PostgreSQL.AI: Anthropic Claude and OpenAI APIs, LangGraph/LangChain.Patterns: DDD in analytics, ports and adapters in the multi-channel audit layer, DI containers. What we're looking for 5+ years shipping production web applications, with real depth on both sides — async Python and React/TypeScript, not one plus a reading knowledge of the other.Frontend: strict-mode TypeScript, React hooks and Context, a modern meta-framework in production, and business logic that lives in domain models rather than components.Backend: async Python with type hints and Pydantic v2, FastAPI-style dependency injection and SSE streaming, SQLAlchemy async with migrations, and PostgreSQL schema design you'd still stand behind in two years.At least one production feature built on an LLM API, with practical handling of tokens, context limits, streaming, timeouts and refusals. LangGraph or LangChain is a plus, not a requirement.Multi-tenant data security as an instinct, and comfort operating alone across several repositories in different languages and architectures.You use AI coding tools daily and review their output as rigorously as your own. What we offer A small, senior team where your work is visible and your decisions matter.Salary from 3.000 - 4.500 EUR gross/month, depending on experience and fit.Fast-growing VC backed startup with international client portfolio.A fun team of experts across creatives, SEO, content, paid media, and developersA modern, well-equipped office in central Vilnius, easy to reach by public transport, with on-site parking availableHybrid working: 4 days in the office, 1 day from home, with flexibility when you need itMacBook or Windows laptop, plus the software and tools you need to do your job wellPublic transport commute coveredDrinks, snacks, fresh fruit, and good coffee available throughout the dayRegular team outings and social activitiesInternal and external training to support your development, we invest in people who want to keep growing