Senior Experience Engineer (FTC)

Callsign; Greater London; On-site; GBP 90,000 - 130,000; Full time

Benefits offered by this job

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 CallsignBank

Employee Volunteering Program

Job summary

Callsign is seeking a product-focused engineer to own a client-facing surface such as the portal, demo and management platform. You will shape MVPs from briefs, define success metrics, and lead live adoption and performance goals.

You will set frontend standards, own end-to-end delivery, and drive AI-enabled workflows with a regulated verification discipline. Strong system design and cross‑team collaboration are essential.

Qualifications

• Must have solid JavaScript/TypeScript and React experience.
• Comfort beyond frontend: API, service, or infrastructure exposure.
• Experience in system design and architecture for cross‑domain features.
• Evidence of AI-native working with verification.
• Ability to design a test approach and defend it.

Responsibilities

• Ship across the stack: TypeScript/React frontends, Node services, API contracts, CI/CD pipelines and deployment tooling.
• Own testing strategy for a surface and drive release quality.
• Lead platform programmes including migrations, test-framework transitions and upgrades.
• Mentor junior team members and translate roadmaps into executable epics.
• Learn domain concepts like fraud, identity and client operations.

Skills

JavaScript/TypeScript

React

API/Backend exposure

System design

AI-native verification

Testing strategy

Product judgement

Frontend estate architecture

Tools

GitLab CI/CD

Terraform

Helm

GitOps

Job description

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

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.

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