A JSON developer works with JavaScript Object Notation (JSON), a lightweight data-interchange format, to build, manage, and troubleshoot data structures and applications. They primarily ensure smooth data transfer between server and client, designing APIs and services that communicate using JSON. They may also develop schemas to structure JSON data and validate it. Additionally, they may be responsible for parsing JSON data into programming languages, debugging JSON code, and integrating third-party APIs that use JSON. They need strong skills in JavaScript and other relevant programming languages, as well as an understanding of RESTful services.