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# Founding Engineer

- **Company:** cinnamon
- **Location:** London, UK
- **Salary:** £80,000.0 - £120,000.0
- **Contract:** Permanent contract
- **Skills:** JavaScript (Programming Language), Application Programming Interfaces (APIs), Artificial Intelligence, Amazon Web Services, Big Data, Cloud Computing, Software Debugging, Python (Programming Language), PostgreSQL, Performance Tuning, Redis, Next.js, Twilio, TypeScript, Web Applications, Core Voice Platform, Datadog, Tailwind, ReactJS, Large Language Models, Technical Debt, Backend, Fastapi, Data Layers, Sentry, Front End Software Development, Api Design, GPT, Data Pipelines
- **Published:** September 15, 2026
- **Apply:** https://www.indeed.com/viewjob?jk=d28966bcbfa94982

## About the Role

* You're genuinely full-stack. You're strongest in TypeScript/React/Next.js, but you're comfortable moving into Python/FastAPI and backend systems when the problem requires it.
 * You've built with LLMs in production. Not just demos. You've worked with orchestration, agents, RAG, streaming responses, evals, structured outputs or human-in-the-loop systems.
 * You have strong product and UX instincts. You care about trust and clarity in AI products and notice when an interface technically works but feels wrong.
 * You can own ambiguous problems. You don't need a perfectly written spec. You talk to the user, work out what matters and make the call.
 * You're good at debugging. You can trace problems through logs, application code, data and LLM behaviour rather than guessing.
 * You're comfortable with data-heavy products. Large datasets, search, dashboards, structured and unstructured information, performance optimisation.
 * You've shipped end-to-end. From API design and data modelling through to a polished customer-facing interface.
 * You move fast. You know the difference between technical debt worth taking and shortcuts that will hurt us later.
 * You want ownership. You're excited by being one of the people responsible for deciding how the product and engineering organisation should work.

We care more about what you've built, how you think and how quickly you learn than where you went to school.

Technical experience we're looking for

Core

 * TypeScript / JavaScript
 * React / Next.js
 * Python / FastAPI
 * PostgreSQL
 * Production cloud infrastructure on GCP or AWS
 * Building and operating production web applications

Strong signals

 * LangGraph, Vercel AI SDK or similar agent / LLM frameworks
 * RAG systems and vector databases such as pgvector or Pinecone
 * LangSmith, Datadog, Sentry or similar observability tooling
 * Tailwind CSS, ShadCN or similar frontend tooling
 * Real-time or streaming applications
 * Experience with large datasets and natural-language search
 * Building products 0 to 1 or scaling an early-stage product

Bonus points

 * Previous founding engineer, early startup engineer or CTO experience
 * You've built AI products used by real customers at meaningful scale
 * WhatsApp Business API, Twilio or other messaging/telephony integrations
 * Strong design or UX background
 * Experience with voice AI, STT/TTS or real-time conversational systems
 * You've worked directly with customers rather than only through product managers
 * You might want to found a company yourself one day

## Description

* Build and evolve the interfaces agency teams use to monitor AI conversations, intervene when needed, configure agent behaviour and understand what's happening across their business.
 * Own onboarding flows, authentication, permissions, admin controls, billing and the day-to-day product surfaces customers live in.
 * Build dashboards and data-heavy interfaces that make large amounts of structured and unstructured information genuinely usable.
 * Design AI-native interfaces with clear status, editable outputs, graceful fallbacks and human-in-the-loop workflows.

Build the systems behind them.

 * Work across our Next.js / TypeScript application and Python / FastAPI services.
 * Build and evolve LLM-powered workflows, agents, RAG pipelines and data layers.
 * Work with streaming responses, structured outputs, tool calling and agent orchestration.
 * Integrate with CRM systems, telephony providers, WhatsApp, SMS, email and the rest of the software estate agencies already use.
 * Work with PostgreSQL, Redis, vector databases and other infrastructure required to make the product reliable at scale.

Own what you ship.

 * Take features from customer problem to architecture to production.
 * Debug production issues across frontend, backend and LLM systems.
 * Own observability, performance and reliability rather than throwing problems over the wall.
 * Make architectural decisions with incomplete information and move quickly.
 * Talk directly to customers when that's the fastest way to understand the problem.
 * Help set the technical bar and shape how the engineering team works as we grow.