About this Software Engineer (Full Stack) role at Callsign

Callsign · Onsite · London, England, United Kingdom

As a Full Stack Software Engineer at Callsign, you will design, build, and maintain end-to-end features spanning our high-throughput Java backend services and modern web interfaces. You’ll work in an Agile, collaborative environment alongside Product, Experience Engineers and QA to deliver secure, scalable, and intuitive digital experiences. You will take ownership of features from architectural design through implementation, testing, deployment, and operational monitoring.

What you'll do

Design, build, and maintain scalable Java-based backend services and modern frontend web applications.
Develop robust RESTful APIs and integrate frontend interfaces seamlessly with backend systems.
Build responsive, accessible, and performant user interfaces using modern web frameworks.
Write clean, testable, and maintainable code across the full stack following engineering best practices.
Collaborate closely with Product Managers, UX/UI Designers, QA, and platform teams to translate user requirements into technical solutions.
Participate in peer code reviews, contribute to architectural discussions, and proactively address technical debt.
Support deployment pipelines, troubleshoot production issues across frontend and backend layers, and drive continuous improvement.

Requirements

3–6 years of commercial full-stack software development experience.
Strong backend expertise in Java, Spring Boot, and RESTful API design; gRPC experience is a plus.
Hands-on frontend experience with modern JavaScript or TypeScript frameworks, preferably React. Commercial experience with Vue.js or Angular is also welcome.
Proficiency in JavaScript, HTML5, CSS3/SCSS, and responsive UI design.
Working knowledge of frontend build tools and package managers such as Vite, Webpack, npm, or yarn.
Solid experience with relational databases such as MySQL, PostgreSQL, or Oracle, and SQL query writing.
Strong understanding of OOP fundamentals, SOLID principles, and data structures and algorithms.
Familiarity with testing frameworks across the stack, such as JUnit, Mockito, Jest, React Testing Library, or Cypress.
Familiarity with Docker, Linux environments, and CI/CD pipelines.
Exposure to microservices architecture.
Awareness of secure coding practices including OWASP Top 10, XSS, CSRF prevention, and secure authentication/token management.
Strong communication, analytical thinking, and collaboration skills.

Good to have :

Experience with Java 17 and Spring WebFlux with Project Reactor, or Java 21+ Virtual Threads.
Production experience with NoSQL systems such as DynamoDB.
Production experience with TypeScript and modern frontend state management such as Redux Toolkit or Zustand.
Familiarity with design systems, component libraries, and tools like Storybook or Figma.
Production experience with microservices architecture, distributed caching with Redis, and event streaming with Kafka.
Familiarity with container orchestration, Kubernetes, Helm, and cloud platforms such as AWS or GCP.
Familiarity with observability and monitoring tools such as Prometheus, Grafana, OpenTelemetry, or Elastic Stack.
Basic understanding of web accessibility and web performance optimisation

Benefits

Pension scheme with Scottish Widows

Private medical cover with Vitality

Life assurance (4x base salary)

Personal Learning & Development Budget

Cycle to Work Scheme

Company Family Leave

25 days annual leave plus Callsign Bank Holiday

Employee Volunteering Program

Ready to apply to Callsign?

Apply to Callsign

About Callsign

At Callsign we are changing identity. We are an identity fraud, authorization & authentication company, solving the challenges that organizations face in getting their users on to & interacting with their digital platforms.

We use deep learning techniques to combine device, location and behaviour datapoints with dynamic policy management and multi-factor authentication, to verify that the user is who they say they are.

Our aim is to make identification more secure and simple – helping everyone to get on with their digital lives in the most seamless and secure way possible. If you’re interested in working for a company that’s changing the face of digital identity globally, then you’re in the right place. We’re a talented team of research scientists, engineers and developers working with the latest technology to help make the digital world a more secure place.

Our Culture

Callsign is a talented team of people who are passionate about their craft and who care about making the digital world more secure. We work collaboratively, adopting agile principles and methodology to develop a reactive and scalable platform that uses the latest technologies. And with regular boardgames nights, pop-up social activities and company parties, it’s easy to meet new colleagues and feel part of the team.

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