Senior Backend Software Engineer
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Requirements
• 3–6 years of professional backend engineering experience You’ve built and shipped production systems that handle real traffic and real money. • Strong fundamentals in system design, data modelling, and API architecture. You can design a service from scratch and reason about its failure modes before you write a line of code. • Experience with Node.js and TypeScript (our primary backend stack), or strong proficiency in a comparable stack with willingness to transition. • Consumer tech background. You’ve worked at a marketplace, fintech, or consumer product company. You understand what it means to build for end users at scale, not internal tooling or enterprise workflows. • Product engineering mindset. You can articulate the business problem your code solves. You’ve worked closely with product and design, and you’ve made trade-offs that balanced user experience with technical constraints. • Startup or scale-up experience. You’ve worked in environments with fast deployment cycles, evolving requirements, and high ownership. You ship, learn, and iterate. • Comfort with ambiguity. You don’t need a detailed spec to start moving. You can take a problem statement and turn it into a working system. • AI first 10x-er. You think about your role as a 10x-er through the lens of AI. You’ve built AI capabilities either in your spare time or in deployment at scale. • Experience with marketplace dynamics: two-sided platforms, pricing, trust, supply-demand matching • Familiarity with international systems and distributed teams across multiple time zones • A genuine excitement for building something from scratch in a category that didn’t exist three years ago. • This Role Isn’t for You If You Want: • Narrow, siloed ownership where you only touch one service and never see the user • Detailed specs handed to you before you start — we define problems together • A slow-moving, highly structured environment with long release cycles • Fully remote work — this team is on-site in London five days a week • Pure infrastructure or platform work with no product exposure • Ready to build the infrastructure for the world’s fastest-growing fashion economy? If you want to work on genuinely hard problems, with a world-class team, at a company that’s tripling annually — we’d love to hear from you. • The Practicalities • Location: London HQ — Heneage Street, E1 (Shoreditch / Aldgate East) • Work model: On-site, five days per week • Level: Senior (L5) • Stage: Post-Series B, hyper-growth • Team: 100+ across London, India, and Pakistan • Stack: Node.js, TypeScript, AI/ML integration • Culture: High ownership, non-hierarchical, fast-moving. Founder-led with strong opinions loosely held.
Responsibilities
• Own the Ecommerce Journey: Design and build the backend systems powering Fleek’s core marketplace — from item discovery and search through to checkout, payment, and post-purchase. These are product features that directly drive GMV. • Integrate AI into the Product: Build the services that connect FleekSort’s AI classification engine to the marketplace experience — ensuring grading, pricing, and categorisation flow seamlessly into listings, search, and buyer workflows. • Design for Scale: Architect systems that handle 500K+ items per month today, with a clear path to millions. Make pragmatic trade-offs between speed of delivery and long-term scalability. • Shape Technical Direction: Contribute to architectural decisions across the backend. Challenge assumptions, propose alternatives, and help define engineering standards for a fast-growing team. • Mentor and Elevate: Support the growth of more junior engineers through code reviews, pairing, and knowledge sharing. Help raise the technical bar across the team. • Collaborate Cross-Functionally: Work embedded with your product manager and designer to define what gets built. Partner with data, AI, and operations teams to turn complex real-world logistics into reliable, scalable software.
Benefits
• Fleek is digitising an industry that has never had technology. There are no existing playbooks for building an ecommerce experience around secondhand fashion at wholesale scale — where every item is unique, inventory is unpredictable, quality is graded by AI, and the supply chain spans three continents. You will be designing how the transaction layer works for a market that hasn’t existed before. • You will be on our Growth team, owning the ecommerce journey from discovery to checkout, payment and credit systems, order management, and seller tools. Your systems will handle 500,000+ items a month today and million+ by the end of the year. • AI is at the core of everything we do, so you’ll work closely with our data and AI teams to build the backend services that connect FleekSort’s classification engine to the marketplace experience. • We’re looking for a product engineer who can think about how systems affect buyers and sellers at scale. You’ll be expected to understand the business problems your code solves — and challenge whether we’re solving the right ones. • What Makes You a Fleek Backend Engineer? • Product-Obsessed Builder: You think about what the seller sees when their inventory goes live, or why a buyer drops off at checkout. You instinctively connect technical decisions to commercial outcomes. • Comfortable with Ambiguity: We’re building systems for workflows that didn’t exist before Fleek. You thrive when the problem is undefined and collaboration is key. • Customer-Focused Thinker: You understand the dynamics of customer platforms and can understand how technical choices affect customers and our broader marketplace. • Owner, Not Renter: You take a feature from problem definition to production and monitor it afterwards. • Startup Pace: You’ve worked in environments where shipping matters more than perfection, where you deploy daily, and where velocity is a competitive advantage. • Fleek is building the AI-native operational and financial backbone for a $350 billion market that has never been digitised. Joining now means you’ll be part of the team that defines how the secondhand economy works — at scale, globally. • The problem is real: 9 million items saved from landfill since 2022. Your work has tangible, measurable impact. • The AI is genuinely novel: FleekSort is an AI model fine-tuned on secondhand fashion, turning an opaque manual trade into a structured global inventory layer. This isn’t a GPT wrapper. • The growth is exceptional: Tripling year-on-year, ~$50M raised, Series B closed. Backed by a16z, Y Combinator, HV Capital, with advisors from Depop, Shopify, and Postmates. • The timing is perfect: The secondhand market is projected to reach $350B by 2027. EU regulation is mandating the infrastructure Fleek builds. You’re catching a wave. • You’ll have real ownership: 100-person company, no bureaucracy. You’ll shape decisions and see the impact of your work immediately. • Five values shape how we work at Fleek: • Dream Big and Disrupt Yourself: Push the most ambitious version of what you’re building. Step out of your comfort zone. Nothing is out of reach. • Absolute Ownership: The buck stops with you. Drive initiatives to completion. Experiment, learn, persevere. The job isn’t done until the job is done. • Curiosity Leads the Way: Don’t accept anything at face value. Ask questions you don’t know the answer to. That’s how you innovate. • Talk to the Customer: Deeply understand their challenges, motivations, and ambitions. Every decision starts with the customer at the centre. • Embrace Diversity: A global team building for a global supply chain. Bring your authentic self and embrace the diversity of everyone you encounter.