YCSB-JSON is an extension of the Yahoo! Cloud Serving Benchmark (YCSB) that enhances its utility for benchmarking JSON databases like Couchbase and MongoDB by supporting complex queries involving arrays, nested objects, joins, and aggregations. It is designed to emulate realistic user scenarios and allows for the generation of datasets using tools like FakeIt, while ensuring queries do not contain hardcoded values. The system operates by generating and loading data into a database, using YCSB to cache and execute queries with non-deterministic predicate values. The YCSB-JSON utilizes generators to create flexible predicates that can be easily integrated with different databases, supporting operations such as pagination and report queries. The implementation details for Couchbase and MongoDB involve specific query structures, and the extension aims to facilitate the integration of new operations and further development of data generation and query predicate tools.