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Software Engineer | Client Side in Madrid or Remote


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Job Description

At Seedtag our goal is to lead the change in the advertising industry, because we believe that effective advertising should not be at odds with users’ privacy.

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 that finds 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 for their brand. All of this, without relying on cookies or any other tracking mechanisms.

Every day, our teams develop new services that reach over 200 million users worldwide with fast response times to ensure that we deliver the best user experience. We’re fully committed to the DevOps culture, where we provide the platform that our Software Developers and Data Scientists use to manage over 100 different microservices, pushing dozens of changes to production every day. All of this is built on top of Kubernetes in Google Cloud Platform and Amazon Web Services.

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.


2014 · Founded by two ex-Googlers

2018 · 16M total turnover & Internationalization & Getting growth

2021 · Fundraising round of 40M€ & +10 countries & +230 Seedtaggers

2022 · More than 70k API requests per second and 3 million messages per second in our Kafka cluster

  • 175TB of events ingested daily by our system
  • +420 Seedtaggers
    • Peaks of more than 2 million messages per second in our kafka cluster
    • 175TB of events ingested daily by our system


  • Outcome over output
  • Failure is allowed, learning is a must
  • We are all boy scouts
  • We are data-driven


We are looking for a talented Software Engineer to join our Engineering team in the Adserving chapter and help us change the world of digital advertising together.

The adserving chapter is in charge of designing the agent that it’s embedded in 200 million devices daily. It’s responsible for orchestrating the monetization of our integrated digital media and the optimization of our branding key performance indicators. In this process the agent it’s also an analytics client with which we harvest data from this environment and user behavioral metrics to later optimize the same process. This team is also in charge of the tools that our design team uses on a daily basis to create the most amazing creatives on the planet. You can’t miss taking a look here and delight yourself.


Our codebase consists of: A multipackage monorepo built with Javascript/Typescript and OCaml/ReasonML/Rescript for our UI’s and the Agent.

Our backend consists of a series of microservices built-in with Typescript and Node.js embracing clean architectures

Our cloud infrastructure runs on Google Cloud. We store data in Redis, MongoDB, GCS, and other storage systems. We love kafka, event-based and data-streaming architecture models, and building great products as fast as possible following the best practices.

Our agent is built in Rescript/ReasonML, an OCaml compiler syntax layer, designed by Facebook’s engineering team, similar to JS that compiles to a very efficient JS and that has a “sound” type system, which means that you'll never see a runtime exception again. This agent is the heart of everything we do. Performance’s key for us. We build our agent with an event-driven architecture in which multiple stateless and stateful services deal with each other.

Our UI components and tools are designed with a declarative approach by using React.js plus modern data management techniques (ReactiveX, GraphQL). We embrace functional programming paradigms: Type driven development, referential transparency, ****purity & effectulness (monadic readers and effects). This allows us to have some benefits that typically arise from doing TDD (test-driven development)

  • Programming mistake detection
  • Promoting a clean, and emerging design
  • Making it so you can refactor without breaking your code
  • Disallowing illegal states in our programs
  • Verifying logic ⇒ For this one we actually ❤️ writing unit and integration tests


  • Have key responsibilities within the design, architecture, and end-to-end delivery of key modules
  • Be obsessed to work on our Agent and Tools and the data produced by them full-time
  • Write clean scalable code and test and deploy applications and systems
  • Contribute to improving the architecture of our Agent, and identify areas of improvement. Enhance the internal API’s design and introduce new modules while improving the design of the overall domain
  • Contribute to increasing our testing environments (QA and AB test) and coverage quota on top of our current Jest and Cypress layer
  • Contribute to the maintenance and speed of our CI pipeline, ensuring that our bundle delivery is fast, performant, and reliable
  • Support, coach, and mentor junior engineers to foster their capabilities and empower them to grow amongst us.
  • Become an authoritative voice for the technical capabilities of our Agent and provide core support and technical evangelism for the rest of the company
  • Apply all the above to some of our domain multidisciplinary squads with other engineers and product people to build world-class products that are used in millions of devices every day



  • You bring more than 3-5 years of programming experience with JS and embrace an Agile mindset in your daily practice.
  • Sound understanding of SOLID principles and good practices
  • Proactive, with strong problem-solving skills, a team player, and fun to work with.
  • You have a strong desire for self-improvement through side projects and sharing
  • You’re obsessed not only with technology but with crafting amazing technology to substantially impact the business
  • Proficiency in JavaScript (ES6), HTML5 and CSS3.
  • Good knowledge of cross-browser compatibility


  • Experience with web scripting or web agent development.
  • Understanding of functional programming idioms like Monads and Functors
  • Understanding of Reactive extensions or Observables
  • Experience in developing complex modular web apps is a plus (especially without frameworks).
  • Knowledge of script performance optimization and Google Core Web Vitals management.
  • Prior exposure to building pipeline design and management for JavaScript bundling.
  • Experience mentoring junior engineers and teams.
  • Knowledge of the principles of UX and attention to detail/product ownership.


We are an AdTech family where innovative ideas and new ways to do things are welcome, we reject "that’s the way it’s always been done". In Seedtag you can find an energetic, fresh workplace, multicultural work environment where our members are from different countries in Europe, LATAM and so many more! where you will have the chance to impact directly on the company results. Everyone is willing to help because we are all committed to a common objective, making Seedtag the best company in the world!

Seedtag DNA is unique from the very beginning, we celebrate and embrace diversity, also we want all our members (They, he or she) to feel at home, and all of the human differences are welcome.


Here at Adserving, you’ll find a team that works and helps each other on challenging problems that require innovative solutions to create/deliver the most amazing ads on the planet. You’ll learn and help to improve our ads developing/serving/testing/monitoring tools and a lot of data-based tools that we use on a daily basis. You’ll learn about reactive patterns, functional programming, key performance metrics optimization cycles, and a lot of new skills that are interesting for any software developer. (Aitor Oses - Ads Chapter Tech Lead)


  • 🚀 Key moment to join Seedtag in terms of growth and opportunities
  • 💼 Carrer ladder plan for your professional growth
  • 💸 High-performance tier salary bands excellent compensation
  • 🏦 Stock option plan for every high performer team member
  • 💯 Seedtag One: Work for a month from any of our open offices with travel and stay paid if you’re a top performer (think of Brazil, Mexico..., 🏖️)
  • 🏉 Paid travels to our HQ in Madrid to work p2p with your squad members
  • 💻 Macbook Pro M1
  • 🏠 Build your home office with a budget of up to 1K (external screen, chair, table...)
  • ⌛ Flexible schedule to balance work and personal life
  • ⛰️ An unlimited remote working environment, where you can choose to work from home indefinitely or attend our Madrid headquarters whenever you want, where you will find a great workplace location with food, snacks, great coffee, and much more.
  • 🎗️ A harassment-free, supportive and safe environment to ensure the healthiest and friendliest professional experience fostering diversity at all levels.
  • 🇬🇧 🇪🇸 Optional company-paid English and/or Spanish courses.
  • 📚 Access to learning opportunities (learning & development budget)
  • 🍻 We love what we do, but we also love having fun. We have many team activities you can join and enjoy with your colleagues!
  • 🍽️🚘 Access to a flexible benefits plan with restaurant, transportation, and kindergarten tickets and discounts on medical insurance

Want to be a Seedtagger? Then send us your CV, we are waiting for it!


About Seedtag

  • Marketing

  • Madrid, Spain

  • 50-200

  • 2014


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