Senior Software Engineer - Fullstack

<p><a href="https://www.fospha.com/">Fospha</a> is dedicated to building the world's most powerful measurement solution for online retail. For over a decade, we've helped teams make smarter decisions with full-funnel marketing insights, forecasting, and optimisation. With Fospha, every team moves faster and grows smarter.</p> <p>Trusted by <strong>leading brands</strong> across three continents, including <strong>Gymshark</strong>, <strong>Huel and Oh Polly,</strong> Fospha <strong>manages $4 billion</strong> in annual ad spend.</p> <p>We're scaling fast across <strong>London, Mumbai, and Austin</strong> – and we're now looking for a Senior Software Engineer to join our Team!</p> <p> </p> <p><strong>The Role </strong></p> <p>As a Senior Software Engineer, you'll build the products our customers rely on every day to make multi-million dollar media decisions. You'll work across the full stack - from crafting responsive, intuitive frontend experiences through to designing and scaling the backend microservices that power them - and, given the seniority of this role, you'll also help shape system design and infrastructure decisions as we scale.</p> <p>You'll work alongside engineers, product managers, and AI agents as part of our AI-first operating model, where lean, high-autonomy teams ship fast and learn faster. This is a hands-on engineering role for someone who's comfortable owning a feature end-to-end - from initial design through to production - and who wants to grow their craft in a fast-moving, ambitious environment.</p> <p><strong>Where you'll focus<br>• </strong>Frontend development using modern JavaScript frameworks (React.js or Next.js)<br>• Backend development using Python-based microservices<br>• System design and infrastructure, contributing to architectural decisions as we scale<br>• End-to-end feature ownership across the stack<br>• (Nice-to-have) Exposure to Data Science / Data Engineering workflows</p> <p><strong>Key Responsibilities<br></strong>• Design, build, and maintain full stack features - from frontend UI/UX through to backend services and APIs in Python.<br>• Contribute to system design and infrastructure decisions, helping evolve our technical foundations as we scale.<br>• Get involved across the full Software Development Lifecycle, from initial planning and design through execution, release, and monitoring in production.<br>• Write clean, well-tested, maintainable code, and champion good engineering practices across the team.<br>• Collaborate closely with product managers, designers, and fellow engineers to translate requirements into working software.<br>• Build and consume APIs (REST/GraphQL) that connect frontend experiences to backend services.<br>• Work with AI agents as part of our AI-first operating model, using clear specifications to shape high- quality, AI-assisted engineering work.<br>• Take ownership of the quality, performance, and reliability of the features you ship.<br>• Participate in code reviews, giving and receiving candid, constructive feedback.<br>• Stay curious about new tools and technologies, including opportunities to explore Data Science / Data Engineering problems as they arise.</p> <p><strong>What are we looking for? </strong></p> <p>• Have around 5+ years of professional experience as a full stack / senior software engineer, with a balanced skill set across frontend, backend, and infrastructure.<br>• Have strong, hands-on experience with front-end technologies such as React.js or Next.js, and solid backend experience building and maintaining Python-based microservices.<br>