A JSON Web Token (JWT) developer constructs and manages secure web tokens used for authentication and data transfer between parties in web applications. They ensure the generation, validation, and decoding of JWTs, and maintain their security. JWT developers also work on server-side logic, implementing user authentication and authorization between multiple systems, servers, and environments. They integrate applications with third-party services and troubleshoot application bugs. Thus, they are pivotal in ensuring the security and integrity of data transmissions in web applications. They often work with other developers, system admins, and cybersecurity professionals in their tasks.