The author of the text has implemented a JSON-based agent using the Mixtral 8x7b LLM, which interacts with a graph database Neo4j through a semantic layer. The agent uses predefined tools to access information and perform actions, such as recommending movies or answering questions about actors. The author used the LangChain framework to implement the agent, which provides a JSON-based prompt structure for the LLM to use when calling tools. The output of the agent is structured in a specific way, including a "Thought" section where the LLM explains its actions and an "Observation" section where it provides tool outputs. The author also implemented a dummy smalltalk tool to handle cases where no action is required. The code for the agent is available as a Langchain template and Jupyter notebook.