Founding Engineer (London)

About Sparkles

Make everyone on your team an engineer

Tech

Sparkles is built for real-time AI agent execution at the edge. **Frontend:** TanStack Start, React 19, TypeScript, Tailwind CSS 4, Radix UI, TanStack Router **Backend:** Cloudflare Workers, Hono, Cloudflare Durable Objects for real-time WebSocket state **Database:** Convex for serverless real-time data, plus Durable Object storage for conversation persistence **AI:** Opencode running autonomously in isolated sandboxes, routed through a dual-auth relay worker with per-model token and cost tracking **Sandboxing:** Daytona cloud sandboxes with snapshot-based fast startup, Docker containers with s6-overlay, and an in-container daemon (Hono + node-pty) that manages Opencode PTY sessions and streams NDJSON events live **Infra:** Cloudflare R2, Stripe + Clerk Billing for credit-based usage, and Sentry + PostHog for monitoring and analytics

The role

**Location:** London · In-person · Full-time\\with relocation to San FranciscoWe're hiring a **founding engineer** who moves fast, cares about craft, and wants real ownership from day one. You'll build side by side with the founders, in person in London, from day one.You should already use AI tools by default — pushing Cursor, Claude Code, Codex, and agent workflows hard, judging output critically, and moving faster without lowering the bar.## What you'll own* Build and ship core product features end to end.* **Talk to users constantly**, find bottlenecks, and ship fixes fast.* Suggest new features, new products, and new internal tooling.* Help **set the engineering bar**, architecture, and pace of the company.* This is not a role where you can coast. It requires deep ownership, **agency**, and responsibility.## What we're looking for* Strong TypeScript and React skills.* Roughly 1–5 years shipping real product software is a good baseline, but we'll flex for someone unusually strong.* Ability to build full-stack product features with high autonomy.* Strong product instincts and a bias toward outcomes.* High agency: you notice problems, propose solutions, and drive things to completion.* **Good design taste.** You can make sensible UI/product decisions, and Figma fluency is a plus.* Clear communication and strong judgment.* Comfort with ambiguity and a founder-speed environment.* Heavy AI-tool usage as part of your real workflow, not as a novelty.## Strong pluses* Experience with **Cloudflare Workers**, Durable Objects, service bindings, realtime systems, or collaborative/live product surfaces.* Experience building devtools.* Experience building sandboxed or safety-sensitive systems.Sparkles was founded by Dan, who dropped out of University College London and previously worked with the former CTO of Monzo at [Iterate.com](http://Iterate.com). **We raised $3.5M, backed by Y Combinator, Moonfire Ventures, and angels from OpenAI, Anthropic, a16z, General Catalyst, Cloudflare, and others.**

Skills

• TypeScript