CosmosDB Emulator is a must have tool if you develop applications for Azure CosmosDB. Also, it’s a great tool to have if you like to learn about Azure CosmosDB but you have limited access to Azure for any reason. Azure CosmosDB team constantly works to make all available tools better including the emulator. Currently, emulator supports SQL, Cassandra, MongoDB, Gremlin and Table API. Data Explorer feature supports only SQL API for now. Emulator’simplementation is different than the service and you should not use it for stress testing, you can not test global replication or latency for read and writes.
It’s also useful for testing scenarios where you want some level of integration testing but don’t want to rely on an external service.