Fullstack Engineer - Ad Serving AdExchange

Overview

Are you ready to engineer the future of the Cookie‑less Web? Seedtag is the leader in contextual advertising. We don’t track users; we understand content. We are looking for an Ad Serving Engineer—a specialist who masters the browser environment but possesses a "system‑level" mindset.

You are a wizard in the browser, but you understand that your code is part of a massive delivery pipeline. You are ready to bridge the gap between high‑performance client‑side scripts and the backend services that power them.

Who we are

We are Seedtag, the leaders of contextual advertising technologies, on a mission to create a better advertising industry that respects users’ privacy and experience. Our machine learning‑based technology combines natural language processing and computer vision to provide a human‑like understanding of web content. We find the best context for each ad and protect advertisers from showing their ads on damaging pages without relying on cookies or 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.

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
• 200 TB of events ingested daily by our system

Speed is critical.

The Mission

You will join the team responsible for our Curation Platform, our inventory integration platform and, most importantly, our Ad‑Serving Client Scripts. This isn’t your typical SaaS; we have thousands of active publishers and our scripts reach over 200 million devices daily.

Your mission is to ensure that our ads render perfectly, fast, and without impact on the publisher’s page performance. While you lead the client‑side logic, you will operate in a fullstack environment, evolving into our Node.js backend to build end‑to‑end features for our delivery engine.

Your Responsibilities

• High‑Performance Ad Tags: Optimize our "Ad Tags" (TypeScript) to ensure seamless rendering across millions of pages. You will deal with cross‑browser compatibility, DOM manipulation, and the Critical Rendering Path where every millisecond counts.
• SaaS & Design Systems: Lead the evolution of our Curation tools using a robust, scalable Design System to ensure a top‑tier UX.
• Fullstack Ownership: Work closely with backend engineers to contribute to the Node.js services. You will help design the APIs that feed our tags, ensuring they are as lean and fast as possible.
• Scalable Architecture: Help us implement DDD (Domain‑Driven Design) and Event‑Driven patterns. We value your frontend expertise here to ensure our APIs are as developer‑friendly as they are fast.

You Will Succeed If

• Browser Internals Mastery: You have 5+ years of experience with TypeScript and deep knowledge of how browsers work (Event Loop, DOM, Web APIs, Security/Sandboxing).
• The Ad Serving Mindset: You understand that "Frontend" in AdTech means building small, highly‑optimized scripts that run on other people’s websites without breaking them.
• The Fullstack "Predisposition": You’re not just a UI developer. You have a strong interest in the backend (Node.js). You view the server as the natural extension of the client.
• SaaS & Design Systems: You have experience building complex B2B platforms where consistency, reusability, and performance are paramount.
• Software Craftsmanship: You advocate for Clean Code and SOLID principles. You believe that "done" includes being well‑tested, documented, and observable.
• Adaptability: You are excited by the idea of moving across the stack. You see the backend as an opportunity to broaden your impact rather than a chore.
• Architecture Awareness: Even if your primary strength is in the client, you understand the principles of building scalable systems. You appreciate why we use Hexagonal Architecture or Clean Architecture to separate business logic from the delivery mechanism. You have a solid grasp in DDD and Event‑Driven Architectures to design resilient APIs.
• AI‑Augmented Productivity: You embrace AI tools (GitHub Copilot, Claude code, LLMs, etc.) as a fundamental part of your daily workflow. You understand how to leverage these tools to speed up boilerplate coding, debugging, and learning, allowing you to focus on high‑level architecture and complex problem‑solving.

Our Tech Stack

Frontend: TypeScript, React, Styled Components / Design Systems.Client‑Side: High‑performance Vanilla JS/TS (Ad Tags).Backend (Where you’ll grow): Node.js, Go, Microservices.Infrastructure: Kubernetes, Kafka, Redis.

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 outcomes rather than just output. 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. We understand setbacks as 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 – We leave 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 proactive initiative.

We are data‑driven – We use data to guide decision‑making, identify opportunities for improvement, and continuously monitor and optimize our systems to deliver the best outcome for our customers.

What else is cool at Seedtag

• Unlimited work from home
• Excellent work/life balance
• Harassment‑free, supportive and safe environment fostering diversity at all levels
• Latest MacBook Pro + 1,000€ for your home setup
• Mentoring and Career development with learning budget
• Restaurant, transport and kindergarten tickets
• Medical insurance discounts
• Free English / Spanish / French lessons
• Paid travel to our HQ in Madrid to gather with your teams
• Paid off‑site meetup with your team, yearly company gathering, Christmas events
• "One Seedtag": a special award that allows you to work for a month from any of our open offices with paid travel and accommodation (think of Brazil, Mexico)

Ready to join?

It’s 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 working on massive scalability challenges, this is the place for you.