Senior Experience Engineer

Who you are

• Solid JavaScript/TypeScript and React
• Comfort somewhere beyond the frontend: an API, a service, or infrastructure
• System design and architecture, designing features that span frontend, service and configuration
• Evidence of AI-native working with stated verification
• A testing instinct: you can design a test approach and defend it
• Has owned a product surface or platform programme including its worst weeks
• Can architect a frontend estate live (state, contracts, testing, deployment)
• Evidence of raising a team's standards
• Demonstrable product judgement
• Java in production; design systems or component library work; SDK or library engineering
• Data visualisation
• Experience in regulated industries (fintech, identity, payments)

What the job involves

• The Experience team owns the human-facing side of Callsign: the client portal, our demo and client management platform (one platform for the whole client journey, from first demo through to proof of concept, onboarding, integration, analysis and ongoing management), the data-product UIs, and the design system and engineering standards behind all of it
• This position is offered as a 12 month fixed-term contract with the successful candidate ideally joining in 2026
• Product & UX
• Own a product surface (portal domain, demo platform, SDK) and holds its product decision right
• Within the direction Product sets, decide what ships and how it works
• Translate a brief into an MVP and phases, define the success measures for what ships, and reshape or kill work that will not move them
• Your surface carries a live measurement baseline (adoption, task success, performance) that decisions cite and post-release reviews are judged against; a decision that would change the direction goes to the PM, not around them
• Propose what to build next from your own product conviction, built from user and client contact, rather than merely executing requests
• Be trusted to ship client-facing work without design review
• Frontend craft:
• Set the technical standard for the estate: your code is the reference
• Lead the response to performance, accessibility or security findings, and anticipate them at design time
• Full-stack:
• Own services and their delivery machinery end-to-end (GitLab pipelines, charts, GitOps, infrastructure)
• Design API contracts consumers can live with long-term
• Execute cross-repo changes (decommissions, migrations) safely across team boundaries
• Lead design review for your surface, where their design docs are the reference alongside your code
• Quality:
• Own testing strategy for a surface, including the release regression cycle: coordinate it, keep it honest, and drives flake to zero rather than tolerating it
• Platform:
• Own platform programmes (package-manager and framework migrations, test-framework transitions, runtime upgrades) end-to-end the plan
• Translate roadmaps into epics others can execute
• Mentor junior team members
• Ship across the stack: TypeScript/React frontends, Node services (with some Java in the portal estate), API contracts, GitLab CI/CD, and deployment via Helm, GitOps and Terraform
• Treat the frontend craft triad - accessibility, performance, security - as engineering, with expectations that rise as you grow
• Build with AI as a core part of your workflow, with the verification discipline a regulated product demands
• Learn the domain deliberately: fraud, identity, authentication, and our clients' operational world, because product decisions made without it are guesses
• Write meaningful tests for everything you ship

Benefits

• Health & wellbeing: From health insurance to discounted gym memberships to childcare vouchers, we constantly invest in the health and wellbeing of our teams
• Learning: Collective growth is one of our core values. Learning opportunities and learning support are core to the Callsign experience
• Family benefit: As well as personal health and wellbeing benefits, we also offer various other discounts like home utilities and childcare vouchers
• Holidays: In addition to 25 days annual leave (on top of bank holidays), you'll also get an additional Callsign bank holiday in June
• Flexible working hours: We've all got different priorities and pressures in our lives. Our flexible working policy will help lighten the load
• Multiple locations: We know that different people work best in different environments – that's why we offer opportunities for flexibility in your working environment