Senior Backend Software Engineer

Job Title:

Senior Backend Software Engineer

- Series B fashion-tech marketplace backed by a16z and YC

You will architect the transaction layer for the world’s first AI-native secondhand fashion marketplace. Reporting to the CTO, you will build scalable systems handling 500k+ items monthly, integrating proprietary computer vision models into core ecommerce flows. This is a high-impact role digitizing a $350B industry while diverting millions of garments from landfills.

London, UK

• Join a hyper-growth Series B startup that has raised ~$50M from top-tier investors including a16z, Y Combinator, and HV Capital.

• Work on Fleek Sort, a proprietary AI model that is fundamentally transforming global supply chains by automating the grading and pricing of unique items at scale.

• Massive environmental impact: the platform has already saved 9 million items from landfills and is tripling in size year-on-year.

• Design and scale backend systems for item discovery, search, and complex multi-continent payment and credit workflows.

• Architect the integration between Fleek Sort’s AI classification engine and the live marketplace to enable real-time inventory structuring.

• Lead technical direction within a senior squad, mentoring junior engineers and defining engineering standards for a rapidly growing 100-person team.

• 3–6 years of backend experience with Node.js and Type Script, specifically building high-traffic consumer marketplaces or fintech products.

• Proven ability to design complex system architectures and data models from scratch while navigating the ambiguity of a fast-paced startup.

• Product-minded engineer who prioritizes commercial outcomes and user experience over pure technical perfection, ideally with interest in AI deployment.

This isn't a trick. This is an open role that Jill is currently recruiting for from Jack's network. Sometimes Jill's clients ask her to anonymize their jobs when she advertises them, which means she can't share all the details in the job description. We appreciate this can make them look a bit suspect, but there isn't much we can do about it.