Freelance Junior Java Developer Jobs in Saint Louis, MO

Our Purpose
Mastercard powers economies and empowers people in 200+ countries and territories worldwide. Together with our customers, we're helping build a sustainable economy where everyone can prosper. We support a wide range of digital payments choices, making transactions secure, simple, smart and accessible. Our technology and innovation, partnerships and networks combine to deliver a unique set of products and services that help people, businesses and governments realize their greatest potential.
Title and Summary
Software Engineer II - Decision Management Program
Position Summary
The Notification Manager team is responsible for Mastercard's enterprise notification platform within the Decision Management Program (DMP). The platform processes high-volume transaction events and delivers customer-facing notifications through email, SMS, and API channels. Engineers on the team build and maintain distributed, event-driven services that support critical fraud, security, and customer engagement products.
As a Software Engineer II, you will contribute to the design, development, testing, deployment, and support of backend services that power Notification Manager. You will work closely with Product, TPMs, Architects, QA, and partner engineering teams to deliver scalable, resilient, and secure solutions while continuing to grow your technical expertise.
What You'll Do
Software Development
• Design, develop, test, and maintain Java/Spring Boot microservices.
• Design software components and service interactions that support scalability, maintainability, and reliability requirements.
• Implement enhancements, new features, and defect fixes across Notification Manager services.
• Participate in technical design discussions and translate requirements into working software.
• Write clean, maintainable, and secure code following Mastercard engineering standards.
• Develop and maintain automated unit, integration, and API tests.
Platform Modernization
• Contribute to modern event-driven architectures utilizing Kafka messaging and distributed processing patterns.
• Contribute to system architecture decisions and technical designs that support platform scalability, resiliency, and long-term evolution.
• Support ongoing platform modernization initiatives, including service decomposition, resiliency improvements, performance optimization, and cloud-native deployment practices.
• Help reduce technical debt and improve operational efficiency across the platform.
Reliability & Operational Excellence
• Participate in production support, incident response, and root cause analysis.
• Monitor system health using observability tools and metrics.
• Analyze application performance and implement improvements to optimize throughput, latency, scalability, and resource utilization.
• Troubleshoot application, infrastructure, and data-related issues.
• Support release activities and production readiness efforts.
• Contribute to operability engineering practices that improve system reliability, monitoring, and supportability.
Collaboration
• Work closely with engineers, QA, PMTs, TPMs, and partner teams to deliver roadmap commitments.
• Participate in Agile ceremonies, elaboration sessions, estimation, and backlog refinement.
• Participate in peer code reviews to ensure code quality, maintainability, security, and adherence to engineering standards.
• Contribute to technical documentation and knowledge sharing.
• Assist and mentor junior engineers where appropriate.
Required Qualifications
• Bachelor's degree in Computer Science, Engineering, or equivalent experience.
• 2-5 years of software development experience.
• Experience developing applications using Java and Spring Boot.
• Understanding of REST APIs and microservice architectures.
• Familiarity with messaging or event-driven systems.
• Strong understanding of software design principles, object-oriented programming, data structures, and algorithms.
• Experience with source control, code reviews, and CI/CD practices.
• Working knowledge of SQL and relational databases.
• Strong troubleshooting and problem-solving skills.
• Ability to work independently on assigned deliverables while collaborating effectively within a team.
Preferred Qualifications
• Experience with event-driven architectures (Kafka, MQ, or similar).
• Experience with cloud platforms, PCF/Tanzu, Kubernetes, or containerized workloads.
• Knowledge of distributed systems concepts including resiliency, fault tolerance, scalability, software architecture, and performance optimization.
• Experience with observability tools such as Splunk, Dynatrace, Grafana, or Prometheus.
• Familiarity with CI/CD pipelines and automated testing frameworks.
• Exposure to PCI, security, or regulatory requirements.
• Experience working in high-volume transaction processing systems.
Success Measures (First 12 Months)
A successful Software Engineer II on the Notification Manager team will:
• Independently deliver stories and enhancements from design through production deployment.
• Contribute meaningful improvements to platform reliability, performance, or maintainability.
• Demonstrate ownership of one or more Notification Manager services or technical domains.
• Participate effectively in production support and incident investigations.
• Build strong partnerships with Product, TPM, QA, and peer engineering teams.
• Continuously improve technical knowledge and contribute to team engineering practices.
Technical Environment
• Java (JDK 17)
• Spring Boot
• Kafka Messaging
• REST APIs
• Oracle / SQL
• GitHub / Bitbucket
• CI/CD Pipelines
• Splunk & Dynatrace
• PCF / Tanzu
• Distributed Event-Driven Architecture
How You'll Make an Impact
You're someone who enjoys backend engineering, solving complex problems, and learning how large-scale distributed systems operate. You are curious, collaborative, and proactive, taking ownership of your work while continuously looking for ways to improve the platform, the codebase, and the team's engineering practices. You apply sound software design principles, contribute to architectural discussions, leverage strong problem-solving skills, and take pride in delivering high-quality, secure, and reliable software solutions.
Mastercard is a merit-based, inclusive, equal opportunity employer that considers applicants without regard to gender, gender identity, sexual orientation, race, ethnicity, disabled or veteran status, or any other characteristic protected by law. We hire the most qualified candidate for the role. In the US or Canada, if you require accommodations or assistance to complete the online application process or during the recruitment process, please contact reasonable_accommodation@mastercard.com and identify the type of accommodation or assistance you are requesting. Do not include any medical or health information in this email. The Reasonable Accommodations team will respond to your email promptly.
Corporate Security Responsibility
All activities involving access to Mastercard assets, information, and networks comes with an inherent risk to the organization and, therefore, it is expected that every person working for, or on behalf of, Mastercard is responsible for information security and must:

• Abide by Mastercard's security policies and practices;
• Ensure the confidentiality and integrity of the information being accessed;
• Report any suspected information security violation or breach, and
• Complete all periodic mandatory security trainings in accordance with Mastercard's guidelines.

In line with Mastercard's total compensation philosophy and assuming that the job will be performed in the US, the successful candidate will be offered a competitive base salary and may be eligible for an annual bonus or commissions depending on the role. The base salary offered may vary depending on multiple factors, including but not limited to location, job-related knowledge, skills, and experience. Mastercard benefits for full time (and certain part time) employees generally include: insurance (including medical, prescription drug, dental, vision, disability, life insurance); flexible spending account and health savings account; paid leaves (including 16 weeks of new parent leave and up to 20 days of bereavement leave); 80 hours of Paid Sick and Safe Time, 25 days of vacation time and 5 personal days, pro-rated based on date of hire; 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; and many more. Mastercard benefits for interns generally include: 56 hours of Paid Sick and Safe Time; jury duty leave; and on-site fitness facilities in some locations.
Pay Ranges
O'Fallon, Missouri: $92,000 - $147,000 USD