Senior Frontend Engineer (React.js)

Who is Castor?

“Castor’s success is due in no small part to our attention to UI & UX. The ability to remain agile in this field is crucial.” 

David Sigley, Head of Engineering at Castor

Castor is a leading cloud-based clinical data platform working with some of the world’s largest medical device companies, biopharma, and renowned academic institutes.

We simplify the clinical trial process, from recruitment to analysis, with user-friendly, patient-centric technology. Our mission is to bring medical research into the digital age. Why? Because medical research is still largely run using free-text, paper, and legacy technology.

Our self-service platform enables our users to run remote, device enabled, patient-centric trials. By helping our users capture high-quality data and making it machine-readable, we are fundamentally changing the flawed evidence-based medicine process.

How is Castor supporting the Coronavirus crisis?

Castor has joined the global fight against the Coronavirus by making our research data capture system available for free for all COVID-19 research projects. Castor is supporting more than 250 COVID-19 studies across the world, including the World Health Organization’s SOLIDARITY trial.

The Role

What you’ll do?

Joining our team as a Frontend Engineer, you’ll have the opportunity to work on a greenfield project and shape Castor’s frontend culture. To make medical research faster and smarter, you will strive to grow an application with the best possible UI and UX on a modern, easy to work with, stack by:

  • Owning and growing our React Front End engineering, moving further towards a well-structured, tested, and accessible experience;
  • Leading our frontend engineers by example, both by mentoring and setting standards through your daily work on features and improvements;
  • Supporting the QA team with the infrastructure that allows them to create End-to-End tests with Javascript;
  • Collaborating closely with our Design System Team to integrate existing components into our application(s) and add new capabilities to this system;

What you’ll work with?

Currently, we are using React, Redux, NextJS, TypeScript. Additionally, we’re using Babel, Webpack, Jest, TestCafe, ESLint, Prettier, SCSS, and other tools. The backend consists of modern PHP7 applications, backed by multi-tenant MySQL databases. Our toolbox includes CircleCI, Github, Slack, JIRA, Storybook, and MkDoc.

What you’ll bring?

As a Senior Frontend Developer, you have extensive experience in building up large-scale Front-End JavaScript Applications. You’re using React with confidence, making the way of working accessible and effective for others, by bringing:

  • Solid experience using React.js, keeping HTML and CSS maintainable and adaptable in large projects;
  • Foundational knowledge about web technologies, such as backend programming languages and tools, web-related protocols, and a general understanding of how the internet works;
  • Fluent verbal and written communication skills in English;

What you’ll get

At Castor, we truly live and breathe our core values, believing we can achieve anything with a "healthy and happy team." With this in mind, we offer the following benefits:

  • A flexible and remote working opportunity (we also have an office in Amsterdam)
  • A competitive salary and a guaranteed 'happy holidays' bonus
  • Investing in our talent with a strong Employee Stock Option Plan
  • 30 days annual leave (including national holidays)
  • Interested in lifelong learning? You’ll love using our development and training budget!
  • Flexible approach to working - nobody is tracking your time except you.
  • A MacBook or Dell laptop, we’re a tech start-up after all ;)
  • Like to feel zen? You’ll love our company subscription to Calm for meditation and yoga

To make medical research smarter and faster, and build top-notch products to support decentralized clinical trials, we pay close attention to diversity & inclusion in Castor’s Product and Engineering teams. You can learn more from our Team Lead Roxana and Software Engineer Luciana Interviews on how they experience working at Castor and their thoughts on D&I challenges.

Want to know more? Check out the role profile for some further insights or apply now!

Castor continues to grow as an Equal Opportunities Employer. We strongly encourage applications from women, people of colour, and people from the LGBTQ(+) community. In your application, please feel free to share the pronouns you use (for example she/her/hers, he/him/his, they/them/theirs, etc).

Our Interview Process


Fill out a short application on our careers website.

Telephone Call
Telephone Call

If your application is successful, we’ll invite you to an intitial call with a member of our talent team.

Manager interview
Manager interview

Great news! You’re invited to meet the hiring team.

Interview Day
Interview Day

Now we’ve got even better acquanted, we’d like to invite you to a final stage interview day.


Congratulations! We’re making you a formal offer to join as our next Castorian!

Meet Your Future Colleagues

Roxana Christian
Roxana Christian
Senior Software Engineer
Sebastiaan Knijnenburg
Sebastiaan Knijnenburg
Principal Innovation Engineer
Bas van Vliet
Bas van Vliet
Senior Software Engineer
© 2021 Castor Careers