Senior Full-Stack Engineer (Backend-Leaning) | Fully Remote (UK hours) |Full-time

Salary: TBC
About the company Our client is a UK B2B SaaS platform for property-investment businesses. Its customers source residential properties for investors, negotiate deals and earn a fee, and the platform helps them find opportunities, manage clients and deals, and market themselves. With around 60 paying customers on a white-labelled GoHighLevel setup, the team is now rebuilding the product from scratch as its own platform, with property search, deal management, portfolio tracking, financial calculators, Claude-powered AI features and Stripe billing.

The role You’ll be the company’s first engineer and technical lead. You’ll own how the platform is built: the data model, security, payments, background jobs, integrations, and what is safe to go live. Your first big milestone is launching the new platform and moving 60 customers off GoHighLevel without losing data. You’ll work alongside the product founder, who builds every day using Claude Code. Your job is to guide him, not replace him: shape his briefs, catch risks early, and make sure his work and yours don’t collide. A part-time QA analyst tests every release.

What you’ll own Technical direction: architecture, data model, security, testing and code review
Approving everything that ships (the product founder signs off on visual changes)
Setting up the test framework (Vitest, Playwright, GitHub Actions as a merge gate)
Foundations: Postgres with row-level security, auth, Stripe billing, background jobs, transactional email and third-party integrations
The launch and customer migration, including a two-week parallel run
Production: error tracking, logging, alerts, incident response, performance and cost control
Documentation, and helping hire and lead the next engineer
Your first 90 days Weeks 1–2: get set up, learn the code and build plan, and ship a small fix
Month 1: become the reviewer for everything that ships and take ownership of security and data protection
Months 2–3: lead the launch and migrate customers across
What you’ll need 5+ years as a professional software engineer, including 2+ years building and running a multi-tenant SaaS product in production
Strict TypeScript, React 19 and the Next.js App Router (Server Components, Server Actions, streaming, caching in Next.js 15/16)
Strong Postgres skills beyond the ORM: schema design, migrations, indexing, query performance and RLS (Supabase a strong plus)
Stripe in production: subscriptions, webhooks, idempotency, usage or credit-based billing
Background jobs and queues (Inngest, Trigger.dev, BullMQ or similar)
Automated testing as a release gate, CI and Vercel preview deployments
Production ownership with Sentry or similar
Daily, disciplined use of agentic AI coding tools (Claude Code preferred; Cursor or Codex fine): small PRs, tests before merge, and you read the diff
Experience reviewing others’ code as the gate to production and mentoring less experienced builders
Nice to have Building features on LLM APIs (Anthropic or OpenAI)
Migrating customers and data between platforms
Working with large external datasets and third-party data APIs
Multi-tenant security fundamentals (OWASP top 10, secrets, audit logging, UK GDPR)
GoHighLevel, Resend, MapLibre, SEO and Core Web Vitals
No property knowledge or visual design skills needed.

The domain will be taught, and the product founder owns design. You’ll thrive here if you are Happy being the only engineer and picking up work without being told. You can explain technical risk in plain English with options and a recommendation, you’ll say when something is a bad idea and then back the decision once it’s made, you ship small and often, and you speak up as soon as something goes wrong.

This probably isn’t for you if you want a team around you or day-to-day management, you’d rather stop a non-developer from building with AI than help him do it well, you’re mainly a front-end specialist, or you’d hold up shipping for weeks over architecture debates.