OnBuy

Role Description OnCommerce is constantly evolving. Everyone here plays a hands-on role in shaping what comes next, building brands that make an impact across global markets. There’s no red tape or rigid corporate structure; just smart people taking ownership and figuring things out as we build something big together. The pace is fast, priorities shift, things aren’t always perfectly set up, and you’ll often need to get stuck in and solve problems. But if you thrive in that kind of environment, you’ll have real influence, real ownership, and the chance to grow with a rapidly scaling business. The Role - End-to-End Engineering Ownership - Design, build, and maintain full-stack solutions across UI, APIs, and backend systems - Translate product requirements, designs, and wireframes into scalable, production-ready systems - Own features from concept → development → testing → release → monitoring - Front-End Excellence - Build responsive, high-performance user interfaces using modern JavaScript frameworks - Translate UI/UX designs into clean, maintainable code - Optimise applications for speed, scalability, and usability - Back-End & Platform Engineering - Design and develop scalable services and APIs - Work across monolith and microservices architecture (Laravel / PHP services) - Maintain and evolve legacy systems while building modern, scalable architecture - Quality & Engineering Standards - Own quality to production — testing is embedded, not a phase - Write and maintain automated tests (unit, integration, end-to-end) - Participate in and lead code reviews to ensure high engineering standards - Debug, troubleshoot, and resolve issues across the stack - Performance & Scalability - Optimise systems for performance, reliability, and scale - Work with large-scale data systems (MySQL, NoSQL, search platforms) - Identify bottlenecks and proactively improve system efficiency - Collaboration & Leadership - Work in cross-functional teams with Product, Design, QA, and other Engineers - Mentor and support less experienced engineers - Communicate technical concepts clearly to non-technical stakeholders Qualifications - Strong full stack engineering experience, owning end-to-end delivery - Proven backend expertise in PHP (Laravel) - Strong JavaScript (ES6+) skills with modern frameworks (React/Vue/Angular) - Experience designing and building RESTful APIs and scalable systems - Experience with MySQL and NoSQL databases (e.g. Couchbase, MongoDB) - Strong understanding of system architecture and microservices - Experience with event-driven systems (e.g. RabbitMQ, Pub/Sub) and cloud environments (GCP) - Familiarity with Docker and CI/CD pipelines - Strong engineering practices: testing, code quality, and production ownership Requirements - Experience in eCommerce or marketplace platforms - Cloud experience (GCP) - Experience with NoSQL (e.g. Couchbase) and Search platforms (e.g. Constructor & Solr) - Experience working in microservices architecture - This role is UK remote role you must be based in the UK and have full right to work in the UK. - The day rate is £450- £600 per day. DOE Please confirm your outside IR35 day rate upon application. This a contract until the end of August 2026 Our Commitment OnBuy is an equal opportunities employer. We are dedicated to creating a fair and transparent workforce, starting with a recruitment process that does not discriminate on the basis of gender, sexual orientation, marital or civil partnership status, pregnancy or maternity, gender reassignment, race, colour, nationality, ethnic or national origin, religion or belief, disability, or age. Just a heads up — we never use WhatsApp or any messaging apps to contact candidates. If someone reaches out this way, it isn’t us and let the recruitment team know.

• Define and enforce clear ownership boundaries across the engineering team, by domain (Buyer / Seller / Platform), holding every contributor accountable regardless of sourcing model (permanent or partner-led) • Track and report Throughput and Instability per domain, so standards are visible and enforceable, not aspirational • Hold delivery consistent through every point of disruption the transformation introduces: nearshore/offshore onboarding, domain moves, headcount change • Partner with the Transformation Lead to ensure structural change doesn't degrade live delivery • Own the engineering standard across both the current platform and the target state • Review the Transformation Lead's roadmap for engineering-standard and operational impact before commitments are made • Own how modern and legacy architecture coexist during migration, guarding against legacy practices and assumptions leaking into the new platform • Lead and develop engineering capability across squads (including DevOps and platform functions) • Coach and support Tech Leads to build consistent leadership standards across teams • Foster a culture of ownership, accountability, and continuous improvement • Identify capability gaps and support hiring, development, and succession planning • Own resource planning, including capacity, skills mix, and on-call structure • Establish and run a two-tier resolver model: Ops on-call for standard support and runbook-driven issues, Product Engineering (Buyer/Seller) as the resolver group for genuine engineering problems • Build rota depth (minimum 3 engineers per domain, or full team where smaller) so resolution doesn't depend on any one individual • Drive a genuinely blameless Post-Incident Review culture, building on the existing Incident Management SOP • Embed secure coding practice, SAST/DAST scanning, and OWASP-aligned standards into the engineering definition of done • Surface security risk in business terms (exposure, cost to fix vs cost to carry) and route it to the appropriate decision-maker, rather than carrying risk-acceptance decisions unilaterally • Identify, log, and manage technical debt within day to day delivery • Escalate strategic trade-offs (rebuild vs patch, roadmap sequencing) to the Solution Architecture Lead, owning visibility and routine remediation rather than the strategic call • Work with Product Owners (Buyer and Seller) to translate roadmap items into scoped, sequenced engineering execution • Own technical design and implementation choices day to day, operating within established architectural patterns without requiring sign-off for routine work • Escalate to Product Owner Heads where scope or trade-off decisions sit above the Product Owner's remit

• Own the end-to-end buyer journey from basket through to successful order placement across multiple brands and markets, ensuring checkout is fast, trusted, resilient, and commercially effective across 21 markets. • Define and own the product vision and roadmap for basket, checkout, account creation, payment methods, APMs, wallets, payment performance, and payment localisation across multiple brands and markets, aligned to company strategy and business Goals. • Translate buyer friction, payment data, market performance, payment method gaps, APM suitability, operational needs, risk considerations, local payment preferences, language and currency needs, and commercial priorities into clear problem statements, user stories, and measurable outcomes. • Continuously prioritise and refine the backlog based on conversion impact, payment success, APM coverage, customer trust, operational efficiency, brand priorities, local market needs, and business value. • Work closely with engineering, QA, design, data, risk, finance, international, customer service, payment partners, acquiring partners, and PSPs to deliver high-quality checkout and payment experiences across brands and markets. • Lead sprint planning, reviews, and backlog refinement to maintain clarity, alignment, and focus for your squad. • Balance delivery speed with long-term scalability, technical health, payment reliability, APM scalability, compliance requirements, currency and language localisation, brand consistency, and operational efficiency.

• You’ll take ownership of how product data is structured, validated, and used across the platform. • Improving how we classify and understand products at scale • Raising the overall quality of catalogue data and defining what “good” looks like • Ensuring product data supports effective search, filtering, and discovery • Identifying gaps in our catalogue and surfacing opportunities for growth • Improving how our catalogue performs across external channels • You’ll build and evolve the systems and decision logic that enable this, and iterate based on real-world performance and data. • You’ll work across: - Structured data (catalogue attributes, GTINs, taxonomy) - Unstructured data (text and images) - Behavioural data (search, clicks, conversions)

• Own GMV growth at target contribution across all performance channels and markets. • Set channel mix, investment guardrails, pacing rules, and scaling strategy. • Partner closely with Finance to forecast spend, GMV, and contribution/ROI • Define segmentation across department, margin band, seller ID, and performance tiers. • Ensure segments are tested & activated across other channels (Channel activation strategy) • Translate propensity and LTV models into activation. • Own incrementality testing and attribution. • Test, try, kill or adopt new growth channels. • Publish monthly performance insights. • Run weekly growth forums – The company has ambitious growth targets and WoW growth is now vital. • Build a lean, automation-focused team.

• This is a critical role responsible for building, scaling, and evolving OnBuy’s core commerce platform across both front-end and back-end systems. • You will own engineering delivery end-to-end; from customer-facing experiences to underlying services and data systems. • You will operate within a cross-functional team and be accountable for shipping high-quality, scalable solutions that directly impact GMV, seller performance, and customer experience. • Design, build, and maintain full-stack solutions across UI, APIs, and backend systems. • Translate product requirements, designs, and wireframes into scalable, production-ready systems. • Own features from concept → development → testing → release → monitoring. • Build responsive, high-performance user interfaces using modern JavaScript frameworks. • Translate UI/UX designs into clean, maintainable code. • Optimise applications for speed, scalability, and usability. • Design and develop scalable services and APIs. • Work across monolith and microservices architecture (Laravel / PHP services). • Maintain and evolve legacy systems while building modern, scalable architecture. • Own quality to production — testing is embedded, not a phase. • Write and maintain automated tests (unit, integration, end-to-end). • Participate in and lead code reviews to ensure high engineering standards. • Debug, troubleshoot, and resolve issues across the stack. • Optimise systems for performance, reliability, and scale. • Work with large-scale data systems (MySQL, NoSQL, search platforms). • Identify bottlenecks and proactively improve system efficiency. • Work in cross-functional teams with Product, Design, QA, and other Engineers. • Mentor and support less experienced engineers. • Communicate technical concepts clearly to non-technical stakeholders.

Who are OnBuy? OnBuy are an online marketplace who are on a mission of being the best choice for every customer, everywhere. We have recently been named one of the UK's fastest-growing tech companies in the Sunday Times 100 Tech list. All achievements we are very proud of, but we don't let that go to our head. We are all laser focused on our mission and understand the huge joint effort ahead of us needed to succeed. Working at OnBuy: . This is a critical role responsible for building, scaling, and evolving OnBuy’s core commerce platform across both front-end and back-end systems. As a Senior Full Stack Engineer, you will own engineering delivery end-to-end; from customer-facing experiences to underlying services and data systems. You will operate within a cross-functional team and be accountable for shipping high-quality, scalable solutions that directly impact GMV, seller performance, and customer experience. This role moves beyond “front-end vs back-end” you are an Engineer responsible for outcomes, not layers. End-to-End Engineering Ownership - Design, build, and maintain full-stack solutions across UI, APIs, and backend systems - Translate product requirements, designs, and wireframes into scalable, production-ready systems - Own features from concept → development → testing → release → monitoring Front-End Excellence - Build responsive, high-performance user interfaces using modern JavaScript frameworks - Translate UI/UX designs into clean, maintainable code - ·Optimise applications for speed, scalability, and usability Back-End & Platform Engineering - Design and develop scalable services and APIs - Work across monolith and microservices architecture (Laravel / PHP services) - Maintain and evolve legacy systems while building modern, scalable architecture   Quality & Engineering Standards - Own quality to production — testing is embedded, not a phase - Write and maintain automated tests (unit, integration, end-to-end) - Participate in and lead code reviews to ensure high engineering standards - Debug, troubleshoot, and resolve issues across the stack   Performance & Scalability - Optimise systems for performance, reliability, and scale - Work with large-scale data systems (MySQL, NoSQL, search platforms) - Identify bottlenecks and proactively improve system efficiency   Collaboration & Leadership - Work in cross-functional teams with Product, Design, QA, and other Engineers - Mentor and support less experienced engineers - Communicate technical concepts clearly to non-technical stakeholders

Who are OnBuy? OnBuy are an online marketplace who are on a mission of being the best choice for every customer, everywhere. We have recently been named one of the UK's fastest-growing tech companies in the Sunday Times 100 Tech list. All achievements we are very proud of, but we don't let that go to our head. We are all laser focused on our mission and understand the huge joint effort ahead of us needed to succeed. Working at OnBuy: We are a team of driven and motivated people who thrive when working at pace. To succeed at OnBuy you need to take charge and fully own your responsibilities, rolling your sleeves up when needed to 'get it done'. Working at OnBuy you are surrounded by so much opportunity, but you must possess the ability to stay focused and prioritise ruthlessly. Most importantly, you will thrive in an ever-changing environment as we are constantly evolving. At OnBuy, you're not just a number or another cog in a machine. We are creating something really special, and you have the opportunity to affect meaningful change and have your voice heard. We are a close team, who have the opportunity to learn and grow as OnBuy evolves. About the Role This is a Contract Role In this newly created role as Senior Performance Marketing Manager your primary responsibility is to maximise incremental GMV and contribution from Google & Bing Shopping/PMax through world‑class campaign architecture, feed intelligence, and efficiency control. Success is measured in incremental revenue and contribution/day, not ROAS. You are OnBuy’s deep technical expert across Google Shopping, Bing Shopping, Search, and PMax. You own and design the entire Shopping ecosystem end‑to‑end: structure, segmentation, labels, feed quality, bidding logic, Merchant Center health, and commercial optimisation. This is a hands‑on individual contributor role, not a strategist position.   Key Responsibilities:  Shopping & PMax Architecture Ownership - Own the full Shopping & PMax architecture, including: - Campaign tiers & priorities - Listing group design - Custom label frameworks - Negative structures - Feed‑driven segmentation - Ensure structural scalability across tens of thousands of campaigns and millions of SKUs, including automation of campaign creation, routing, and lane governance.” - Control the interplay between PMax and Standard Shopping, ensuring optimal margin, traffic shaping, and signal control. - Design and maintain complex, feed‑driven segmentation frameworks for millions of SKUs, including product eligibility tiers, performance cohorts, and commercial signals. - Architect and manage multiple optimisation environments to ensure clean Smart Bidding signals, scalable growth across product groups, and controlled exploration. - Own CSS account strategy including bid separation logic, feed‑exclusion rules, and optimisation of commission/auction mechanics. Feed, Merchant Center & Diagnostics - Own full Merchant Center health: schema, feed rules, disapprovals, diagnostics, and error remediation. - Build and maintain advanced labelling systems for commercial signals, product scoring, seller quality, and activation logicTranslate commercial conditions (margin, fee bands, seller activation) into schema logic. Contribution & Incrementality Optimisation - Optimise towards incremental GMV and contribution, not ROAS. - Use propensity modelling outputs, EXTA parameters, decile segmentation, and SKU-level economics to shape structure and bids. - Lead the Daily Trading Room: identify opportunities, isolate issues, and deploy rapid interventions. - Work with Data/BI teams to operationalise performance‑based product movement rules, activation logic, and automated routing systems that dictate bidding exposure Efficiency & Wastage Reduction - Own wastage elimination across: - Query sculpting - Negative structure hygiene - Asset group discipline - Budget pacing rules - Low-value SKU suppression - Implement robust recovery and oxygen playbooks for campaigns requiring stabilisation. - Own campaign‑lane health: monitor lane density, merge/split structural segments as needed, and maintain strong learning conditions across very large SKU sets Measurement & Technical Leadership - Own and improve tracking approaches across PMax, Shopping Profit frameworks, and revenue tracking systems. - Ensure structure and tracking changes are documented, measurable, and repeatable. - Partner with Data Science to operationalise propensity segmentation. - Own end‑to‑end conversion tracking integrity, including server‑side conversions API, GTM audits, feed attribution, and ongoing monitoring of tracking capture rates vs internal GMV   Vendor, Automation & Partner Governance Manage and commercially challenge third‑party Shopping vendors and automation partners, including audit of bidding decisions, versioned change‑history accountability, and validation of performance claims

Who are OnBuy? OnBuy are an online marketplace who are on a mission of being the best choice for every customer, everywhere. We have recently been named one of the UK's fastest-growing tech companies in the Sunday Times 100 Tech list. All achievements we are very proud of, but we don't let that go to our head. We are all laser focused on our mission and understand the huge joint effort ahead of us needed to succeed. Working at OnBuy: We are a team of driven and motivated people who thrive when working at pace. To succeed at OnBuy you need to take charge and fully own your responsibilities, rolling your sleeves up when needed to 'get it done'. Working at OnBuy you are surrounded by so much opportunity, but you must possess the ability to stay focused and prioritise ruthlessly. Most importantly, you will thrive in an ever-changing environment as we are constantly evolving. At OnBuy, you're not just a number or another cog in a machine. We are creating something really special, and you have the opportunity to affect meaningful change and have your voice heard. We are a close team, who have the opportunity to learn and grow as OnBuy evolves. This is a critical role responsible for building, scaling, and evolving OnBuy’s core commerce platform across both front-end and back-end systems. As a Senior Full Stack Engineer, you will own engineering delivery end-to-end; from customer-facing experiences to underlying services and data systems. You will operate within a cross-functional team and be accountable for shipping high-quality, scalable solutions that directly impact GMV, seller performance, and customer experience. This role moves beyond “front-end vs back-end” you are an Engineer responsible for outcomes, not layers. End-to-End Engineering Ownership - Design, build, and maintain full-stack solutions across UI, APIs, and backend systems - Translate product requirements, designs, and wireframes into scalable, production-ready systems - Own features from concept → development → testing → release → monitoring Front-End Excellence - Build responsive, high-performance user interfaces using modern JavaScript frameworks - Translate UI/UX designs into clean, maintainable code - ·Optimise applications for speed, scalability, and usability Back-End & Platform Engineering - Design and develop scalable services and APIs - Work across monolith and microservices architecture (Laravel / PHP services) - Maintain and evolve legacy systems while building modern, scalable architecture   Quality & Engineering Standards - Own quality to production — testing is embedded, not a phase - Write and maintain automated tests (unit, integration, end-to-end) - Participate in and lead code reviews to ensure high engineering standards - Debug, troubleshoot, and resolve issues across the stack   Performance & Scalability - Optimise systems for performance, reliability, and scale - Work with large-scale data systems (MySQL, NoSQL, search platforms) - Identify bottlenecks and proactively improve system efficiency   Collaboration & Leadership - Work in cross-functional teams with Product, Design, QA, and other Engineers - Mentor and support less experienced engineers - Communicate technical concepts clearly to non-technical stakeholders

Who are OnBuy? OnBuy are an online marketplace who are on a mission of being the best choice for every customer, everywhere. We have recently been named one of the UK's fastest-growing tech companies in the Sunday Times 100 Tech list. All achievements we are very proud of, but we don't let that go to our head. We are all laser focused on our mission and understand the huge joint effort ahead of us needed to succeed. Working at OnBuy: We are a team of driven and motivated people who thrive when working at pace. To succeed at OnBuy you need to take charge and fully own your responsibilities, rolling your sleeves up when needed to 'get it done'. Working at OnBuy you are surrounded by so much opportunity, but you must possess the ability to stay focused and prioritise ruthlessly. Most importantly, you will thrive in an ever-changing environment as we are constantly evolving. At OnBuy, you're not just a number or another cog in a machine. We are creating something really special, and you have the opportunity to affect meaningful change and have your voice heard. We are a close team, who have the opportunity to learn and grow as OnBuy evolves. This is a critical role responsible for building, scaling, and evolving OnBuy’s core commerce platform across both front-end and back-end systems. As a Senior Full Stack Engineer, you will own engineering delivery end-to-end; from customer-facing experiences to underlying services and data systems. You will operate within a cross-functional team and be accountable for shipping high-quality, scalable solutions that directly impact GMV, seller performance, and customer experience. This role moves beyond “front-end vs back-end” you are an Engineer responsible for outcomes, not layers. End-to-End Engineering Ownership - Design, build, and maintain full-stack solutions across UI, APIs, and backend systems - Translate product requirements, designs, and wireframes into scalable, production-ready systems - Own features from concept → development → testing → release → monitoring Front-End Excellence - Build responsive, high-performance user interfaces using modern JavaScript frameworks - Translate UI/UX designs into clean, maintainable code - ·Optimise applications for speed, scalability, and usability Back-End & Platform Engineering - Design and develop scalable services and APIs - Work across monolith and microservices architecture (Laravel / PHP services) - Maintain and evolve legacy systems while building modern, scalable architecture   Quality & Engineering Standards - Own quality to production — testing is embedded, not a phase - Write and maintain automated tests (unit, integration, end-to-end) - Participate in and lead code reviews to ensure high engineering standards - Debug, troubleshoot, and resolve issues across the stack   Performance & Scalability - Optimise systems for performance, reliability, and scale - Work with large-scale data systems (MySQL, NoSQL, search platforms) - Identify bottlenecks and proactively improve system efficiency   Collaboration & Leadership - Work in cross-functional teams with Product, Design, QA, and other Engineers - Mentor and support less experienced engineers - Communicate technical concepts clearly to non-technical stakeholders