Senior Fullstack Software Engineer

This position is listed on behalf of a partner company, who manages all applications and next steps. Our partner is looking for a Senior Fullstack Software Engineer based in Brazil. This is an opportunity for a senior engineer to build and evolve scalable, reliable fullstack applications within a data-driven technology environment. You will work across frontend and backend layers, contributing to products that help businesses make better-informed decisions. The role combines hands-on software development with a strong focus on application performance, reliability, monitoring, and production excellence. You will use technologies such as ReactJS, NodeJS, NestJS, MongoDB, and PostgreSQL to deliver robust SaaS and platform solutions. Beyond feature development, you will investigate incidents, perform root cause analysis, and help strengthen systems against future failures. You will collaborate closely with engineering teams in an agile environment where clean code, testing, scalability, and continuous improvement are highly valued. This role is well suited to an experienced fullstack engineer who enjoys solving complex technical challenges and building dependable products at scale. Design, develop, maintain, and continuously improve scalable, reliable, and efficient fullstack applications using ReactJS, NodeJS, NestJS, MongoDB, and PostgreSQL. Build high-quality frontend and backend solutions while ensuring smooth integration across application layers. Optimize application performance, scalability, and resource efficiency to support reliable platform growth. Contribute to the reliability and efficiency of system infrastructure and help identify potential areas for improvement. Implement and maintain continuous monitoring, alerting, and observability practices to proactively identify system issues. Collaborate with engineering teams to diagnose and resolve performance bottlenecks and production incidents. Conduct root cause analysis of production errors and implement corrective measures to prevent recurring issues. Develop and maintain unit tests and apply software engineering best practices to ensure code quality, maintainability, and reliability. Use Git effectively for source control, code collaboration, and development workflows. Contribute to technical decisions and continuous improvements across SaaS and platform-based solutions. Requirements: At least 5 years of professional experience in fullstack software development, with strong hands-on experience in ReactJS and NodeJS/NestJS. Strong proficiency in developing, maintaining, and optimizing applications using MongoDB and PostgreSQL. Solid understanding and practical application of software engineering principles such as SOLID and Clean Code. Experience working with SaaS products and/or platform-based solutions. Knowledge of unit testing practices, libraries, and methodologies. Strong experience with Git and collaborative software development workflows. Good understanding of monitoring, observability, incident response, and production troubleshooting. Strong English communication skills, both written and verbal. Ability to investigate complex technical problems, identify root causes, and implement sustainable solutions. Collaborative mindset, strong ownership, analytical thinking, and a commitment to engineering quality. Knowledge of Docker and Kubernetes is a plus. Previous experience with AI development tools is desirable. Experience with event-streaming technologies such as Kafka is an additional advantage. Benefits: Remote work opportunity from São Paulo, Brazil. Contractor employment model. Opportunity to work within a data and technology-driven environment serving businesses across Latin America and the Caribbean. Exposure to modern fullstack technologies, SaaS and platform solutions, cloud-native practices, and scalable systems. Opportunity to contribute to products where reliability, performance, and data-driven decision-making are core priorities. Collaborative engi