Senior Software Engineer - C# / Java

About the Position

We are seeking a Senior Software Engineer with 5-8+ years of experience in C# and Java to join our global team in the United Kingdom.

About Threecolts

Threecolts is a software suite built for consumer brands, helping them recover revenue, operate more efficiently, and grow across major retailers and marketplaces. Our largest business, Margin Pro, helps brands recover money owed to them by retailers and marketplaces such as Amazon, Walmart, and Target by managing disputes on their behalf. Alongside this, we’re building and scaling newer products, including AI Operator and Retail 365, while continuing to grow our portfolio of subscription products across our customer base.

Responsibilities

• Take ownership of features across Inventory Lab’s C# and Java-based systems, delivering them from initial design through to production.
• Design and build clean, scalable services, APIs, and components that are maintainable, well-tested, and performant.
• Operate independently within a defined scope, making sound technical decisions and balancing speed with long-term quality.
• Play an active role in improving the systems you work on, debugging production issues, identifying root causes, and implementing durable fixes.
• Contribute to technical discussions, help evolve architecture within your domain, and raise the bar through thoughtful code reviews.
• Collaborate closely with Product, QA, and DevOps to build features and improvements that deliver meaningful value to Inventory Lab customers.

Requirements

• 5–8+ years of professional software engineering experience
• Strong proficiency in C# and Java
• Experience building and maintaining backend services, APIs, and scalable application components
• Solid understanding of REST APIs, system design, and scalable application patterns
• Experience working with SQL databases and data modelling
• Familiarity with cloud infrastructure, ideally AWS
• Experience debugging production systems and resolving issues independently
• Comfortable working with Git, code reviews, and team-based development
• Ability to work across an existing codebase and improve quality without over-engineering

We Offer

• Salary: £110,000 per year
• 25 days PTO
• Healthcare & Pension benefits
• Opportunity to join company-wide offsites
• Regular rate reviews and bonus opportunities
• Fully remote/hybrid working

About the Company

We’re a global team of 340 people across 33 teams, having grown through 24 acquisitions. We operate with a flat structure, giving people real ownership and the ability to move quickly. AI is embedded in how we work across the business, helping us increase speed, improve quality, and operate at scale.

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