Help us build the engine that powers Contextual Advertising at scale.
Seedtag is the leader in Contextual Advertising. We are on a mission to create a better advertising industry by respecting user privacy while delivering high-impact results through AI. To do this, we need a Mid-Senior Backend Engineer who is passionate about high-performance systems, clean architecture, and solving complex data challenges in real-time.

Who are we?

We’re the leaders of Contextual Advertising Technologies. At Seedtag our goal is to promote a better advertising industry where effective ads respect the user’s privacy and experience.

By combining Natural Language Processing and Computer Vision, our proprietary Machine Learning-based technology provides a human-like understanding of the content of the web. We find the best context for each ad, while providing unparalleled risk-mitigation capabilities that protect advertisers from showing their ads on pages that could be damaging to their brand. All of this, without relying on cookies or any other tracking mechanisms.

We are a scale-up in a hyper-growth phase so we need to ensure that our product can scale up, and we need your brain for this.

We want you to innovate and we have plenty of space for you to develop professionally.

What are our challenges?

…in numbers:

• We handle more than 180 billion events per day

• We process on average 600,000 web pages per hour

• Our CDN serves 1.5 petabytes every month to 200 million devices worldwide

So… it’s all about speed.

Your mission (if you accept it) is to make our platform… Harder, Better, Faster, Stronger.

The Mission

You will join the AdExchange Engineering Team, the "engine room" of Seedtag. Your primary focus will be Inventory Management and Bid Enrichment.

This is a high-stakes environment where you will build the logic that categorizes global ad inventory and enriches bidding requests with real-time contextual data. You will work in a high-throughput ecosystem where we don't just "deliver code"—we form hypotheses, measure real business impact, and iterate with an agile mindset to optimize our auction win rates and revenue.

Your Challenges

Inventory & Bid Enrichment: Own the core services that manage our global ad inventory and enrich bids with contextual metadata. This is a critical "hot path" in our infrastructure where low latency is non-negotiable.

High-Performance Node.js: Utilize Node.js, TypeScript, and Fastify to build ultra-low-latency services capable of handling hundreds of millions of requests daily.

Architectural Excellence: Lead the way in applying Hexagonal Architecture and Domain-Driven Design (DDD) to ensure our AdExchange remains maintainable and scalable as we grow.

Event-Driven Systems: Design and evolve our data pipelines using Kafka, ensuring that bid enrichment and inventory updates are processed reliably and asynchronously.

Technical Ownership: You will be responsible for making key technical decisions, managing project timelines, and collaborating with Data and Product teams to drive the project forward.

Quality & Observability: Ensure our services are not only fast but also resilient, well-tested, and fully observable through robust monitoring and logging practices.

You Will Succeed If

The 5-Year Milestone: You have 5+ years of demonstrable experience in software engineering, with a focus on building high-performance backend systems.

Node.js & TypeScript Expert: You have a deep understanding of the Node.js event loop and asynchronous programming. Experience with Fastify is a significant plus.

Architectural Practitioner: You don't just know the theory; you have experience implementing Hexagonal Architecture (Ports & Adapters) and DDD. You know how to define clear domain boundaries and isolate business logic from infrastructure.

Distributed Systems Knowledge: You are comfortable with Event-Driven Architectures and message brokers like Kafka. You understand the challenges of eventual consistency and distributed data.

The "Big Picture" Thinker: You understand the business context of your work. You can balance the need for "perfect code" with the pragmatic need to deliver value and iterate based on data.

Software Craftsmanship: You are an advocate for Clean Code, SOLID principles, and TDD. You take pride in producing code that is easy for your peers to read and maintain.

Curiosity for Go: While our core stack for this role is Node.js, we have services in Go (Golang). You don't need to be an expert, but you should be excited to learn and contribute to our Go codebase when needed.

AI-Driven Efficiency: You see AI as a partner in engineering. You actively use AI tools to increase your productivity, from generating unit tests to refactoring legacy patterns. You are curious about how AI can help us build more resilient systems faster and you stay updated on the best ways to integrate it into a professional SDLC.

Our Tech Stack

Primary: Node.js, TypeScript, Fastify
Secondary: Go (Golang)
Data & Messaging: Kafka, MongoDB, Redis
Infrastructure: Kubernetes, AWS, Terraform
Patterns: DDD, Hexagonal Architecture, Event-Driven Microservices

Our core engineering values

Outcome over output

Our core engineering values reflect our commitment to delivering exceptional results, fostering a culture of continuous learning, and always putting the customer's needs first. We believe that success comes from focusing on the outcomes rather than just the output. Our engineering team aims to solve problems that make a meaningful difference, and we measure our success by the impact we have on the customer.

Failure is allowed, learning is a must

We also recognize that failure is an inevitable part of the innovation process. Our team understands that setbacks are opportunities to learn and grow. We believe in testing early and often, and we continuously iterate and improve until we arrive at the best solution.

We are all boy scouts

Another core value we hold is that we are all boy scouts. We believe in leaving things better than we found them. This means we take ownership of our work and strive to improve the systems and processes we touch. We encourage our team members to be proactive in identifying areas for improvement, and we value those who take the initiative to implement positive changes. Our goal is to leave a lasting, positive impact on our projects and our team.

We are data-driven

Lastly, our team is data-driven. We believe that making informed decisions based on data is crucial to our success. Our engineering team uses data to guide our decision-making process and to identify opportunities for improvement. We are committed to using data to continuously monitor and optimize our systems and processes to ensure that we are delivering the best possible outcome for our customers.

What else is cool at Seedtag?

Unlimited work from home
Excellent work/life balance
Harassment-free, supportive and safe environment to ensure the healthiest and friendliest professional experience fostering diversity at all level
Latest Macbook Pro + 1,000€ for your home setup
Mentoring and Career development with learning budget
Restaurant, transports and kindergarten tickets
Medical insurance discounts

… but there is more!

Free English / Spanish / French lessons
Paid travel to our HQ in Madrid to gather with your teams
Paid offsite meetup with your team, Christmas events
"One Seedtag": a special award which allows you to work for a month from any of our open offices with paid travel and accommodation (think of Brazil, Mexico...)

It's really a key moment to jump in the bandwagon with us and join the Seedtag adventure. If you are interested in joining one of the fastest growing startups in Europe and work on massive scalability challenges, this is the place for you.

#MeaningfulWork #LoveToCode #FeelAtHome #EmbracingChange #DeepThinker #WeAreGlobal #ContinuousLearning #FailFastLearnFast #WeAreFamily #BornContextual