Senior Software Engineer

Mastercard•O'fallon, MO

32d•$115,000 - $184,000•Onsite

About The Position

Join Mastercard’s Transaction Stream team in O’Fallon, MO, and help build the applications and services that power critical capabilities across the real-time payment network. This is an opportunity to work on software that operates at global scale, where speed, reliability, and resilience matter every day. As a Senior Software Engineer, you will collaborate with engineers and product partners to design, build, test, and enhance solutions that support the movement of transactions around the world.

Requirements

Experience building applications and REST APIs using Java, Spring Boot, and Spring Data JPA
Strong foundation in computer science fundamentals, including data structures, algorithms, and object-oriented design
Ability to write clean, secure, testable code and contribute to unit, service, and integration testing.
Comfort working with SQL and relational data concepts.
Strong analytical and problem-solving skills, with the ability to debug issues and identify practical solutions.
Strong verbal and written communication skills and the ability to work effectively in a collaborative team environment.
Self-motivated, organized, and eager to learn, with a passion for continuous improvement and delivering results.
Strong hands-on experience in software engineering, including development and quality engineering
Proven experience working with: Testing across platforms: Linux and web applications
Automation development and CI/CD integration and deployment (Jenkins / XLR) and code coverage tools (Sonar, Clover) to ensure high code/ conditional coverage
Unit, functional, and integration testing
Performance testing and engineering
Strong knowledge and understanding of: Software design principles (OOP, modularity, design patterns)
Software architecture concepts (microservices, distributed systems, scalability)
Data structures and algorithms
Experience with secure coding practices and application security principles (e.g., OWASP)
Ability to contribute to system design and architecture decisions

Nice To Haves

Experience in cloud and microservices architecture or mainframe modernization
Experience designing systems for reliability, performance, and scalability
Domain knowledge in payments and transaction processing systems
Bachelor’s or master's degree in computer science or equivalent experience is preferred

Responsibilities

Design, develop, and maintain scalable test frameworks and automation solutions aligned with enterprise architecture standards
Apply software design principles and architectural patterns to create maintainable and extensible testing and validation systems
Contribute to system architecture discussions, ensuring solutions are testable, observable, secure, and performant
Translate business and system requirements into well-designed technical solutions, test strategies, and validation models
Ensure secure coding practices are embedded in development and testing processes, proactively identifying vulnerabilities and risks
Develop and execute testing strategies across all levels: unit, functional, integration, system, and performance testing
Leverage data structures and algorithms to optimize test execution, data handling, and performance validation
Collaborate in Agile environments, contributing to backlog refinement, sprint planning, and design discussions
Design, build, test, deploy, and maintain software components, automation frameworks, and validation tools
Apply strong knowledge of data structures, algorithms, and efficient coding practices in building scalable solutions
Contribute to end-to-end software development lifecycle, including design, development, testing, deployment, and monitoring
Participate in defining software architecture and design patterns to ensure scalability, reliability, and maintainability
Ensure systems are designed for testability, observability, performance, and operational readiness
Provide input into microservices and cloud migration strategies
Develop and implement test automation frameworks and CI/CD integration pipelines (e.g., Jenkins, XLR)
Design comprehensive test strategies and plans, including performance, reliability, and production simulation testing
Ensure high code quality and coverage using tools such as Sonar or Clover
Apply and promote secure coding practices, including code analysis, vulnerability detection, and mitigation strategies
Integrate security testing into CI/CD pipelines
Conduct and lead code reviews, ensuring adherence to coding standards, security practices, and maintainability
Act as a technical reviewer for system designs, test strategies, and implementation approaches
Ensure systems are observable, monitorable, and resilient across environments
Perform performance engineering, including load testing, tuning, and bottleneck analysis
Troubleshoot complex production issues and ensure rapid resolution
Partner with developers, architects, and product teams to drive engineering best practices
Mentor junior engineers and contribute to knowledge sharing across teams
Evaluate and recommend tools, technologies, and frameworks for continuous improvement

Benefits

insurance (including medical, prescription drug, dental, vision, disability, life insurance)
flexible spending account and health savings account
16 weeks of new parent leave
up to 20 days of bereavement leave
80 hours of Paid Sick and Safe Time
25 days of vacation time
5 personal days
10 annual paid U.S. observed holidays
401k with a best-in-class company match
deferred compensation for eligible roles
fitness reimbursement or on-site fitness facilities
eligibility for tuition reimbursement