Senior Experience Engineer (FTC)

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.

The candidate will already need to hold the right to work in the UK.

What you'll do

• 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

Requirements

Key Responsibilities

• 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.

Required Skills & Experience
A must:

• 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

Nice to have:

• Java in production; design systems or component library work; SDK or library engineering
• Data visualisation
• Experience in regulated industries (fintech, identity, payments).

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