Senior Backend Software Engineer (£100k–£140k + Equity) at $50M Series B AI-native marketplace

This is a job that Jill, our AI Recruiter, is recruiting for on behalf of one of our customers.

She will pick the best candidates from Jack's network.

The next step is to speak to Jack.

Job Title

Senior Backend Software Engineer

Salary

£100k–£140k + Equity

Company Description

$50M Series B AI-native marketplace backed by a16z and Y Combinator

Job Description

You will join the Growth squad to build the transaction layer for the world’s first digital supply chain for secondhand fashion. Reporting to the CTO (ex-Google, Postmates), you will integrate fine-tuned AI models into a B2B marketplace handling 500,000+ items monthly, turning manual trades into a structured, searchable global inventory layer.

Location

London, UK

Why this role is remarkable

• Work at the intersection of circular economy and proprietary AI, using a fine-tuned model (not a GPT wrapper) to digitize a $350B industry that has never had technology.
• Massive financial backing with ~$50M raised from elite investors including a16z, Y Combinator, and HV Capital, plus advisors from Depop and Shopify.
• High-velocity environment where you will see immediate impact, helping save millions of garments from landfills while the company triples in size year-on-year.

What You Will Do

• Architect and scale backend systems in Node.js and TypeScript to handle the transition from 500k to millions of unique items per month.
• Own the end-to-end ecommerce journey, including discovery, search, checkout, and complex international payment and credit systems.
• Collaborate with AI and data teams to bridge the gap between classification engines and the core marketplace product experience.

The ideal candidate

• 6–10 years of professional backend experience with strong fundamentals in system design and API architecture at high-growth consumer or marketplace companies.
• Proven product engineering mindset with a history of shipping end-to-end features in fast-paced, ambiguous startup environments.
• AI-forward builder who uses tools like Cursor or Copilot as a force multiplier and has experience deploying AI capabilities at scale.

Who are Jack & Jill?

Ok, I'll go first. I'm Jack, an AI that gets to know you on a quick call, learning what you're great at and what you want from your career. Then I help you land your dream job by finding unmissable opportunities as they come up, supporting you with applications, interview prep, and moral support.

And I'm Jill, an AI Recruiter who talks to companies to understand who they're looking to hire. Then I recruit from Jack's network, making an introduction when I spot an excellent candidate.

How does this work?

• Jack's an AI agent for job searching and career coaching. He works for you.
• Jill is the AI recruiter working for the company. She recruits from Jack's network.
• If it's a match and the company wants to meet you, they'll make the intro. In the meantime, if you'd like, Jack will send you excellent alternatives.

We never post fake jobs

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.

Give Jack a spin! You could land this role. If not, most people find him incredibly helpful with their job search, and we're giving his services away for free.