A JSON/XML developer works with JSON (JavaScript Object Notation) or XML (eXtensible Markup Language) data formats to build, design, and maintain systems for data interchange and storage. They create and implement strategies to integrate, manipulate, and manage data from various sources. They are involved in data validation, parsing, serialization, and deserialization. They also work with APIs, ensuring seamless data exchange between servers and users. Their role may involve collaborating with other developers, troubleshooting, and optimizing systems for improved performance. Their work is crucial in web development, data analysis, and application development.