Senior Full-Stack Engineer – AI-Driven Development (m/f/d)

Your role

• You will co-own an area of our media-planning platform, such as Media Planning, Reporting Center, Data or our API, together with a small team of engineers and client relations, end to end across backend and frontend

• AI agents write most of our code. You decide what gets built and how it fits together, turning customer needs and business outcomes into clear direction

• You will look after the long-term health of your area: its architecture, its quality, and how well it serves our users

• You will still work hands-on where people matter most, such as debugging production, handling customer escalations, and making tricky design decisions

• You will work closely with users, client relations, and the other teams

• You will help shape how we work with AI. Our process changes as the tools improve, and we expect it to keep changing

• This role can be done remote within Germany or from our modern office in Hamburg

What you bring

• You have solid experience building and running complex web applications, backend and frontend. You need to know what good code looks like to spot it in code you didn't write yourself

• You have very good knowledge of Ruby on Rails, Phoenix Framework, or a similar web framework

• You have good knowledge of a frontend framework such as React, Vue.js, or Angular

• You have good knowledge of a relational database such as PostgreSQL

• You have hands-on experience with AI coding agents such as Claude Code, Codex, or Cursor, and a realistic sense of where they do well and where they go wrong

• You communicate clearly, especially in writing

• You care about tests, maintainability and architecture, and you're comfortable saying no to a change that works but doesn't fit

• You enjoy talking to users and turning vague requirements into concrete acceptance criteria

• You are fluent in English and/or German. Our company language is English, so German is not required

• Knowledge of Elm, Elixir, or multi-tenant SaaS applications is a plus, as is experience in media or advertising.

• Work permission and residence in Germany or willingness to relocate to Germany

You don't tick every box? Apply anyway. We'd rather meet an ambitious, sharp mind who has never written a line of Elm than someone who ticks every box but doesn't fit our team. How we build software Our platform is split into areas such as Media Planning, Reporting Center, Data, API and Media Mix Modelling. Each area is owned by a small, stable team of people who know it deeply, even though they don't type most of the code themselves.

• People set direction, agents implement. The hard part is no longer typing code. It's knowing what to build and keeping the platform coherent. That's where you spend your time.

• Leadership sets direction, teams set the order. Leadership describes outcomes: what success looks like, not how to get there. Your team decides what to work on and in which order.

• Few meetings. Each team keeps its own backlog and meets when it needs to. No long planning documents, no multi-week development cycles, no formal team lead. The team makes decisions together.

• Small things just get done. A customer-reported bug with a small, contained fix doesn't wait for a meeting.

• How hard it is to undo decides who decides. Decisions that are easy to undo are made by the team. For the ones that are hard or expensive to undo, we bring in leadership before we commit.

• Ownership means looking after an area, not guarding it. Any team can change any area, and lets the owning team know.

Nobody has fully figured out how to run engineering with AI agents yet, including us. We keep improving our process as we learn, and you'll help shape it.

• Remote, but not apart. We are a remote (within Germany) company but still value face to face meetings such as our monthly company meeting, parties, game nights or cultural events. Every employee is welcome to work from our beautiful office in Hamburg. However, we see it as everyone's own responsibility to decide how often they want to visit our office.

• Fast, written communication. As knowledge transfer is even more important in a remote environment, efficient and fast communication is a key factor for us. For this purpose we use Slack as our main communication tool.

• Decisions as a team. Teamwork is an essential part of our culture. Every area team makes decisions together, and teams can call an ad-hoc meeting or bring in people from other teams whenever that helps. We stay on an area long enough to know it really well, and move between areas over time to share knowledge and get fresh ideas.

• Flexibility for families. We highly value self-responsibility and flexibility which is reflected in our flexible working times and independent task completion. As we are very family-oriented and many of us have children, we know that a certain degree of work flexibility helps a lot combining private obligations with work life.

• Room to grow. At MMT, we appreciate passion and growth. This is why we like to help everyone to be the best version of themselves. For this reason, we have regular appraisal, feedback and development talks where needs can be placed. We offer many opportunities for growth such as visiting conferences, trade shows, tech-events or other training options, and time to try out new AI tools and ways of working. No formal team lead doesn't mean no growth: you grow by owning more, such as a larger area or decisions that are harder to undo.

Who you'll work with We see our diversity as a key factor of our success and continuing growth. Our team currently includes 9 different nationalities and 17 different languages, which is why we have chosen English as our common corporate language. This diversity of cultural and professional backgrounds allows us to bring different perspectives and innovative solutions to the table. Each team member brings a unique set of experiences and ideas that enrich the way we work and help us respond creatively to challenges.

As a tech company, we know that our industry tends to be male-dominated. Therefore, it is important for us to make working at MMT attractive to all genders and to meet their different needs. At MMT, everyone should have the same opportunities, regardless of gender, because we are convinced: Diversity leads to better ideas, innovations and ultimately to our joint success.

• Backend: Ruby on Rails, Elixir

• Frontend: Elm, Tailwind CSS

• Database: PostgreSQL

• Infrastructure: Kubernetes, Helm, GitLab CI/CD, Terraform

• AI: Claude Code, with shared skills and plugins that we maintain as a team

What we offer

• A salary of €60.000–€90.000 per year, depending on experience

• Small and international teams where you can actually make a difference

• The opportunity to offer modern and leading solutions in an exciting industry

• A modern workplace in the center of Hamburg

• Flexible working hours with remote work up to 100%

• A laptop running Linux or Mac

• Company-paid access to leading AI coding agents

• A subsidized ticket for public transportation (Deutschlandticket)

• Subsidized gym membership (Hansefit)

• Job bike leasing

• Company pension scheme

• Space and time for personal growth and learning new things

You have kids, live far away, or prefer a non-normative lifestyle – we'll make it work! How to apply We try to keep our process as fast and smooth as possible, and we want you to enjoy getting to know us.

• Initial contact

• Chemistry meeting with our Director Software Engineering

• In-depth interview with a member of the team you'd work with

• Trial work day, so we can get to know you as a person and how you work, and you can get to know us

• Feedback / offer

• Onboarding

Questions before you apply? Contact Ole, Director Software Engineering, ole. reifschneider@getmercury. io Who we are MMT builds software that helps media agencies and advertisers plan, run and measure their campaigns, from planning and budgets to reporting. Founded in 2016 as a spin-off of one of Germany's largest independent media agencies, we are now around 30 people, most of us in development.

Want to know more? Visit our careers page or read what employees say about us on kununu. Non-discrimination policy Mercury Media Technology GmbH & Co. KG does not and shall not discriminate on the basis of race, color, religion (creed), gender, gender expression, age, national origin (ancestry), disability, marital status, or sexual orientation, in any of its activities or operations. These activities include but are not limited to, the hiring of staff, selection of vendors, and provision of services. We are committed to providing an inclusive and welcoming environment for all members of our staff, clients, subcontractors, and vendors.