Senior Full Stack Developer React/FastAPI/Django (Frontend-Affinity) (m/f/d)

mika is revolutionizing financial management for small businesses with an AI-powered platform that combines automated accounting, proactive insights, and conversational AI. We're on a mission to make expert financial navigation and compliance accessible to every small business owner – dramatically reducing costs and bureaucratic burden. We're a small, senior team shipping fast, and every line of code we ship matters.

Our stack: FastAPI & Django backend, React frontend (Material UI, react-query), PostgreSQL, AWS. We build agentic AI systems that do real accounting work.

Tasks

We need a Senior Full-Stack Developer who leans frontend – someone who makes our product look and feel as good as it works under the hood.

You'll own features end-to-end. That means you think through the entire user flow, edge cases, error states, and architecture before you start building. You work with high autonomy and take real ownership – we trust you to make good decisions and deliver clean solutions.

Concretely, you'll:

• Drive frontend improvements – not just fixing bugs but proactively elevating UX and visual quality on a regular cadence
• Build and own complex full-stack features in our accounting platform
• Use Claude Code, Cursor, or similar AI engineering tools as your primary development workflow – we are a senior team where everyone writes high-quality code at a high pace, and this is only possible through the use of the latest coding tools. You'll get access to all the subscriptions you need to work efficiently
• Adapt and extend our Python/FastAPI & Django backend where needed (CRUD-level changes and beyond)
• Contribute to code quality and architecture decisions in a small senior team

Requirements

• Professional experience in software development with a proven track record of owning and delivering complex projects.
• Expertise in React to build high-quality, accessible, and production-ready user interfaces.
• A sharp eye for design that ensures layouts and components are implemented with pixel-perfect accuracy.
• Hands-on skill with AI-assisted engineering using tools like Cursor, Claude Code, Codex, or GitHub Copilot. You have already built real things with those tools.
• The ability to work across the stack by independently navigating and extending a Python/FastAPI backend.
• A systems-thinking mindset to map out full features, edge cases, and failure modes before writing any code.
• Fluency in English, while any knowledge of German is a welcome bonus.

Nice to have:

• Background in agentic AI systems or LLM-powered products.
• Familiarity with B2B fintech, PostgreSQL, or German accounting standards like DATEV.

Benefits

• A small team of strong, senior engineers who respect each other's time.
• Real autonomy and ownership from day one.
• Work that's genuinely hard and interesting – German tax law + AI agents is not a solved problem.
• Competitive salary and a product that's actually used by real customers daily.
• Almost no meetings – on average 95% focus time per day.
• 100% Remote option, option to work abroad and no minimum required office attendence.
• Fully flexible working hours apart from Daily Standup.
• Berlin location preferred but remote possible.

1. 📲 Quick intro call with Lisa (~15 min)

A brief introductory call with Lisa, our internal recruiter. She'll walk you through the process, answer any initial questions, and make sure we're aligned on basics like timeline and expectations.

2. 📲 Intro call with the hiring manager (~30 min)

You'll meet with Henry, mika's CTO, to talk about your background, what drives you, and what you're looking for. We'll share more about mika's mission, our team culture, and the role. This is also your opportunity to ask questions about the company and our vision.

3. 🧑‍💻 System design interview with a senior engineer (60 min)

A deep-dive technical session run by one of our senior engineers. We'll give you a real-world scenario and explore how you approach system design from scratch – service boundaries, data models, database design, code-level structure, and tech stack decisions. We want to understand how you think about complex systems, not just whether you know the right answers.

4. 🔍 Code review challenge with the hiring manager (60 min)

This is the core of our technical assessment and reflects how we actually work today. You'll receive a large, LLM-generated microservice – the kind of output our agents produce daily. You'll have ~20 minutes to go through it, then walk us through:

• What you'd fix and why
• What you'd prioritize and what you'd consciously skip
• How you'd approach a PR of this size in a real codebase

We're not looking for perfection. We're looking for judgment, prioritization, and the ability to navigate large codebases efficiently.

5. 👥 Team meeting (~30 min) - optional

A casual call with a few of our engineers – no agenda, no evaluation criteria. Just a chance to get to know the people you'd be working with every day, and for the team to get to know you.

6. 🤝 Founder call (30 min)

A final conversation with one of mika's other founders. This is less about technical skills and more about values, long-term goals, and mutual fit. You'll get a broader picture of where mika is heading and have space to ask anything that's still on your mind.

We aim to complete the entire process within 2–3 weeks. We know candidates are often in multiple processes at once, and we're happy to adapt the timeline or order of steps where needed.