GraphKer is a free and open-source tool that provides a detailed and updated cybersecurity graph database using Neo4j. It aims to find connections between huge amounts of data, providing connectivity and knowledge extraction from these data sets. GraphKer uses a new ontology approach for data feeds to reinforce the knowledge extraction ways that graph databases provide. To run GraphKer, one needs to download and install Neo4j, create and configure the database, install Python requirements, and install applications created for Neo4j. After running GraphKer, users can explore their data in Neo4j graphs, extract knowledge from connected graphs, and analyze cybersecurity incidents, threat actors, hardware, software, skills required, attack paths, etc., to update their cybersecurity level and operational readiness.