Full Stack Engineer in London

At Affinity Labs, we’re building a full-stack AI venture studio that partners with content creators to co-found authentic, scalable software businesses. By combining AI-native development with creator-led distribution, we are pioneering a new model of monetisation by rapidly building, launching, and scaling digital ventures alongside creators and their audiences. We aim to launch ventures 10x faster and cheaper than traditional methods using our internal "AI factory": a multi-agent architecture, reusable component libraries, and a growing knowledge graph that learns from every product we ship.

Why Affinity Labs: Ship at rapid pace with AI-accelerated workflows, see your work distributed to tens of thousands of users at launch, and compound impact across multiple products, not just one.

Role Description: You’ll lead end-to-end product engineering across our portfolio: scoping features, designing APIs and data models, building backend services, and shipping polished user-facing experiences across web and mobile. This is an early-stage, hands-on role with significant autonomy and responsibility. You will own full-stack product delivery, from infrastructure and AI integrations through to React / React Native interfaces, collaborating closely with founders, creators, product, and design to turn lean specs into scalable, user-loved software. We’re looking for a strong generalist with backend depth and real mobile experience.

Responsibilities:

• Implement features end-to-end (mobile web frontend → APIs → data models → integrations) while maintaining quality and velocity.
• Build React Native mobile apps and shared component systems across products.
• Design and ship scalable backend services (APIs, integrations, AI workflows).
• Run tight build → test → iterate → ship loops; provide realistic estimates and surface blockers early.
• Manage tech debt pragmatically.
• Participate in daily standups and weekly planning; contribute to technical strategy and execute from Linear tickets.
• Contribute meaningfully to product and architecture discussions; be heard in debate and align to unified decisions.
• Own operability: CI/CD, monitoring/alerting, performance optimisation, safe rollbacks.
• Build and integrate AI features (LLM/agent workflows, RAG/vector DB integration, eval hooks, cost/safety guardrails).
• Help evolve our reusable product templates and shared architecture across the portfolio.

Essential Requirements:

• 3-6 years building production-grade full-stack applications, with clear ownership.
• Strong backend experience in Python (FastAPI preferred) and solid database skills (PostgreSQL/MongoDB).
• Proven experience building and shipping mobile apps with React Native.
• Strong React fundamentals (Next.js experience a plus).
• Solid API design and systems thinking.
• Familiarity with AWS serverless patterns and Docker; basic CI/CD concepts.
• Comfortable with Redis (caching/sessions) and queue/messaging patterns.
• Startup mindset: high ownership, comfort with ambiguity, bias toward shipping.
• Growth mindset & flexibility: open to feedback; not rigid about stack/tools.
• Clear communicator & collaborator; able to guide product decisions from engineering perspective.
• Evidence of shipping quickly in small teams (links to apps, repos, case studies, live products).

Desired:

• Node.js alongside Python for services or integrations.
• App Store / Google Play release experience.
• Experience with vector databases (e.g., Chroma) and embedding pipelines.
• LangChain or CrewAI for orchestration; MCP servers for integrations.
• Security hygiene (secrets, permissions, least-privilege) and practical data-privacy basics.
• Planning & execution in Linear (or similar).

Tools & Stack:

• Backend/Runtime: Python (FastAPI), Node.js.
• Frontend: React/Next.js.
• Mobile: React Native.
• Datastores: PostgreSQL, MongoDB (as appropriate), Redis (caching/sessions).
• Vectors/Embeddings: Chroma (or similar).
• AI Models & APIs: Claude (Anthropic), Gemini (Google); Amazon Nova Canvas (vision), Deepgram (audio).
• AI Dev Tools: LangChain or CrewAI (orchestration), MCP servers (integration), GitHub Copilot / Claude Code.
• Infrastructure: AWS (serverless functions), Docker (primarily for custom MCPs).

Competencies & Behaviours:

• Communicates clearly with technical and non-technical teammates.
• Takes ownership from concept to deploy and through maintenance.
• Thinks in systems design for reuse across a portfolio.
• Balances technical excellence with pragmatic delivery to meet business needs.
• Adapts quickly to changing requirements and emerging tech; applies AI learnings.
• Sets clear goals, tracks progress, and hits commitments; collaborates across disciplines.

Why this role is a career launchpad:

• Own the code & the company. You step in as a Founding Engineer with a meaningful equity stake from day one.
• Ship faster with AI at your side. Our workflow bakes in AI so you spend your time solving real problems—not boilerplate.
• Ride a rocket. Our wider vision is big and the bar is high; we need driven people who can help us achieve an ambitious roadmap.
• Grow like crazy. You’ll architect, build, and launch multiple products each year. The shipping reps you’ll get in 12 months here would take 3–4 years in a typical startup. There’s a lot of work, it’s high intensity, and the expectation is to ship extremely quickly.
• Learn from builders, not bosses. Work shoulder-to-shoulder with a team that has scaled VC-backed startups, closed multi-million-pound term sheets, and collaborated with 1,000 creators across formats and categories.