Sr. Software Engineer, Fullstack (UK)

Who We Are At Firstup, our mission is to improve the employee experience at every moment that matters, large and small. As the communication pipeline for the world's workforce, we now serve 40 of the Fortune 100 companies, reaching and connecting more than 17 million employees daily. Our employees are experts in the employee experience, workforce communications and technology. Joining Firstup means joining a movement to make work better for every worker. As the world’s first intelligent communication platform, Firstup meaningfully engages employees at every moment from hire to retire, and delivers engagement insights to help companies support, promote and retain their talent. Our movement has taken root and is evident in our world-class customer base. Now we need your help. Ready to make a difference in the world? Job Summary The Sr. Software Engineer will join the team responsible for Firstup's public APIs, Agentic tools, third-party integrations with enterprise systems such as HRIS platforms, and shared platform services. You will deliver innovative, scalable solutions while constantly improving our approach to architecture, scale, availability, and fault-tolerance. You are an active user of Generative AI tools and coding agents, applying them daily to accelerate delivery and improve code quality. Responsibilities Design, build, and maintain public-facing APIs and Agentic tools that enable enterprise customers to integrate with and extend the Firstup platform. Develop and own integrations with external enterprise systems, including HRIS platforms such as Workday, SAP SuccessFactors, and Dayforce. Build and maintain shared platform services used across the wider engineering organisation. Write high-quality code (reliable, readable, efficient, testable, scalable, maintainable), provide thorough code reviews, and create comprehensive tests and documentation. Apply broad, in-depth knowledge to develop and maintain large-scale multi-tenant services in the cloud. Actively use Generative AI tools and coding agents in day-to-day workflows to improve code quality and accelerate delivery. Collaborate across teams on industry standards and best practices to help others solve complex problems. Design future-ready solutions and address architectural gaps using modern microservices and cloud-native patterns. Own production health for your services, contributing to on-call rotations, incident response, and post-incident reviews in a "you build it, you run it" environment. Identify, analyse, and resolve system availability, reliability, and performance issues, contributing to observability and resiliency improvements. Partner with Product Management and Design to translate business requirements into scalable technical solutions. Minimum Qualifications Bachelor's degree in Computer Science or related field, or equivalent experience. 5+ years building reliable, performant applications and microservices. Strong proficiency in TypeScript and Node.js. Ruby experience is a plus. Proven full-stack experience across frontend (React.js), backend, and database layers. Technical depth in at least one specialisation: networking, security, serverless, event streams, or similar. Strong AWS experience, including compute, storage, networking, and monitoring. Excitement to build beautiful, intuitive products with a strong customer focus. Innate curiosity and a desire to learn and teach. Preferred Qualifications: Experience building and maintaining integrations with HRIS platforms such as Workday, SAP SuccessFactors, Dayforce, or similar enterprise HR systems. Experience with Kubernetes, Docker, and Helm. Experience with Datadog or similar observability and monitoring platforms. Demonstrated use of Generative AI tools or coding agents in development workflows. Experience in enterprise SaaS organisations, particularly HR Tech or regulated domains. Familiarity with ML/AI integration in production systems. Open-source contributions or a history of side projects. Why Firstup? Because you care - about people, the work you do, and the connections you make. Work is such a large part of life; it only makes sense to make it awesome. If you want to engage brilliant minds in a high-growth and inclusive environment where ideas are rewarded regardless of who they come from, join us. This is a rapidly changing space so if you thrive on ambiguity, are hungry for a challenge, and have the guts to speak your mind, you could be a perfect fit. We offer an excellent PTO program, great health benefits, a casual and friendly environment, remote work, and a leadership team who truly believes in your growth – both personally and professionally. Firstup is committed to providing equal employment opportunities to all applicants for employment and to all employees, without regard to race, color, religion, gender, sexual orientation, gender identity or expression, national origin, age, protected disability, veteran status, or any other protected status in accordance with applicable federal, state or local laws. #LI-TM1 #LI-Remote